Introduction
Many people classify themselves and others in age-classified groups such as “elderly” and “middle-aged.” These age classifications influence the perceptions and attitudes that people form about themselves and others. In today’s modern and advanced world, socio-economic development has led to a decrease in population growth and an increase in life expectancy, so currently, the growth of the elderly population is more than the overall growth of the world population. The current research was conducted to compile and explain the pattern of teenagers’ and young people’s perceptions of old age. The understanding of old age refers to each person’s knowledge of his aging process in the context of the social culture in which he is located. Old age requires paying attention to all aspects of awareness, understanding, experience, evaluation, interpretation, and recognition of the stages of old age.
Methods
This study was qualitative research using the Grounded Theory method in 2018 in Tehran. Sampling was done purposefully. The data was collected through semi-structured interviews with 20 teenagers (10 girls and 10 boys) and 17 young people (8 girls and 9 boys) until information saturation was reached. The interview was semi-structured. During the interview, the interviewer asked questions to the interviewee in sequence, and a tape recorder recorded his answer. Each of the questions was re-answered and flexible to new questions. Each interview lasted approximately 30 minutes and was then implemented by the researcher. 
The collected data were analyzed and reported in three stages open coding, central coding, and selective coding. In the axial coding stage, the categories were organized. The categories were connected using a variable. In the last stage, i.e., selective coding, one category is considered more important among the categories, and the others are related to it somehow, so a theory is made and discussed. To increase credibility in this research, several methods have been used. 
Long-term engagement and continuous observation were used by the researchers in this study to validate the obtained data. Peer review was another method used to increase the scientific accuracy of the research. After collecting and analyzing the data, the review was reviewed by a colleague who had experience in qualitative research, with critical questions and challenged the data analysis. Review by participants was also used to increase the validity of data analysis. To comply with ethical considerations, at the beginning of the interview, full explanations were given to the interviewees about the purpose of the research, the interview method, and ensuring the confidentiality of the information and their right to participate or not participate in the study.
Results
 The results included 121 concepts, of which 84 concepts were obtained from interviews with teenagers and 37 from interviews with young people. After analyzing and categorizing the concepts, 32 subcategories were received, of which 18 subcategories are related to teenagers, and 14 subcategories are related to young people; finally, 5 main categories were obtained: 3 main categories related to teenagers and 2 main categories related to it was for young people. 
The final model indicated that adolescents’ perception of old age was associated with interpersonal, intra-personal, external, promising, and frightening challenges. Adolescents perceive old age in three categories and subcategories: 1. Interpersonal challenges, “family relationships, quality of socialization, family system dynamics, relationships with others, and family challenges”; 2. Intra-individual challenges: “future-oriented behaviors, adaptation to old age conditions, intra-psychological processes, individual indicators, constructive thoughts, destructive thoughts, fearful thoughts, hopeful thoughts, death and loneliness, mental confusion and mental stability”; and 3. The external challenges were “attention to physical health and livelihood challenges.”
Young people’s perception of old age in two primary and secondary classes, such as 1. promising challenges: “attention to the family, the quality of passing the previous stages of life, personality traits, learning and effectiveness, the quality of the family system, constructive thoughts, success and value, satisfaction and psychological integrity and family support”; and 2. the daunting challenges were “destructive, passivity and physical disability, physical challenges, psychological challenges, and death.”
In the semantic continuum and storyline, finally, the core category (phenomenon) of research for teenagers was placed in two semantic continuums, frightening or hopeful. The nuclear category for young people was also in a semantic continuum between passivity and physical disability and success and value. The pattern obtained from the coding of the interviews shows the mutual effects of the background conditions and action/reaction with the causal conditions leading to the formation of the perception of the phenomenon of old age. Interactions related to the causes, contexts, and action/reaction create situations where a person’s perception of old age is either positive, i.e., promising in teenagers and successful and valuable in young people, or negative, i.e., frightening in teenagers and passivity and physical disability in young people. Following this positive or negative perception, the resulting consequences will be positive or negative.
Discussion
This study, to achieve the research goals and answer the basic questions “what is the pattern of perception of teenagers and young people about old age and what is the difference between the process of perception of old age in teenagers and young people,” the required information is collected and analyzed in the Grounded Theory. The final model extracted shows significant similarities between the process of understanding old age in teenagers and young people. Although the age and lived experience of people in the youth group is more than that of the adolescent group, the semantic and perceptual structure of these two groups is close to each other in the content field of concepts. In the comparison between the pattern of perception of old age in teenagers and young people, although in terms of the frequency and semantic diversity of the categories, slight differences are observed; however, in terms of the process of formation and movement of the final pattern, there is no difference between the two groups.

Ethical Considerations
Compliance with ethical guidelines
All ethical principles were considered in this article. The participants were informed about the purpose of the research and its implementation stages; they were also assured about the confidentiality of their information; Moreover, They were allowed to leave the study whenever they wish, and if desired, the results of the research would be available to them.

Funding
This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.

Authors' contributions
Conceptualization: Mohammad Kahrbai; Methodology: Abdullah Motamedi and Javad Changi; Research: Mohammad Kahrbai and Javad Changi; Writing the original draft: Mohammad Kahrbai and Javad Changi; Written, reviewed and edited by: Mohammad Kahrbai; Sources: Javad Changi; Supervision: Abdullah Motamedi.

Conflicts of interest
The authors declared no conflict of interest.


References

1. Foroughan M, Mohammadi Shahbolaghi F. [Perception of healthy lifestyle among Iranian elders: A qualitative research (Persian)]. Salmand: Iranian Journal of Ageing. 2016; 10(4):132-9. [Link]
2. Sadegh Moghadam L, Foroughan M, Mohammadi F, Ahmadi F, Farhadi A, Nazari S, et al. [Aging perception in older adults (Persian)]. Salmand: Iranian Journal of Ageing. 2016; 10(4):202-9. [Link]
3. Safarkhanlu H, Rezaei Qahroudy Z. [Developments in the population of the elderly in iran and the world (Persian)]. Amar. 2017; 5(3):8-16. [Link]
4. Motamedi A. [Aging psychology(Persian)]. Tehran: Samat Publications, 2017. [Link]
5. Shinan-Altman S, Werner P. Subjective age and its correlates among middle-aged and older adelts. The International Journal of Aging and Human Development. 2019; 88(1):3-21. [DOI:10.1177/0091415017752941] [PMID]
6. Garstka TA, Schmitt MT, Branscombe NR, Hummert ML. How young and older adults differ in their responses to perceived age discrimination. Psychology and Aging. 2004; 19(2):326-35. [PMID]
7. de Freitas MC, Queiroz TA, de Sousa JA. [The meaning of old age and the aging experience of in the elderly (Portuguese)]. Revista da Escola de Enfermagem da U S P. 2010; 44(2):407-12. [DOI:10.1590/S0080-62342010000200024] [PMID]
8. Banks J, Breeze E, Cheshire H, Cox K, Demakakos P, Emmerson  C, et al. Retirement, health and relationships of the older population in England: The 2004 English Longitudinal Study Of Ageing (Wave 2). London: The Institute for Fiscal Studies; 2006. [Link]
9. Janecková H, Dragomirecká E, Holmerová I, Vanková H. The attitudes of older adults living in institutions and their caregivers to ageing. Central European Journal of Public Health. 2013; 21(2):63-71. [DOI:10.21101/cejph.a3774] [PMID]
10. da Silva Mda G, Boemer MR.The experience of aging: A phenomenological perspective. Revista Latino-Americana de Enfermagem. 2009; 17(3):380-6. [DOI:10.1590/S0104-11692009000300016] [PMID]
11. Ingrand I, Houeto JL, Gil R, Mc Gee H, Ingrand P, Paccalin M. The validation of a French-language version of the Aging Perceptions Questionnaire (APQ) and its extension to a population aged 55 and over. BMC Geriatrics. 2012; 12:17. [DOI:10.1186/1471-2318-12-17] [PMID] [PMCID]
12. Abbasi M, Adavi H, Hojati M. [Relationship between religious beliefs and psychological health through purposefulness intermediation in life and aging perception in retired teachers (Persian)]. Ravanshenasi Piri. 2016; 2(6):195-204. [Link]
13. Levy BR, Myers LM. Preventive health behaviors influenced by self-perceptions of aging. Preventive Medicine. 2004; 39(3):625-9. [DOI:10.1016/j.ypmed.2004.02.029] [PMID]
14. Klusmann V, Sproesser G, Wolff JK, Renner B. Positive self-perceptions of aging promote healthy eating behavior across the life span via social-cognitive processes. The Journals of Gerontology: Series B. 2017; 74(5): 735-44. [DOI:10.1093/geronb/gbx139] [PMID]
15. Okoye UO, Obikeze DS. Stereotypes and perceptions of the elderly by the youth in Nigeria: Implications for social policy. Journal of Applied Gerontology. 2005; 24(5):439-52. [DOI:10.1177/0733464805278648]
16. Corbin J, Strauss A. Basics of qualitative research: Techniques and procedures for developing grounded theory. New York: Sage publications; 2015. [Link]
17. Haghi Asgarabadi F, Kraskian Azizari A, Jamhari F. [Determining the psychometric characteristics of the aging perception questionnaire in Iranian elderly (Persian)]. Ravansanji. 2017; 6(22):59-76. [Link]
18. Masoudnia E. [Perceptions and beliefs on aging and their impact on elderly general health: An appraisal of self-regulation model (Persian)]. Salmand: Iranian Journal of Ageing. 2016; 11(2):310-21. [DOI:10.21859/sija-1102310]
19. Bastani F, Beigi Boroujeni P. [The association between the perception of aging and functional independence in the elderly patients with type II diabetes mellitus (Persian)]. Iran Journal of Nursing. 2019; 32(117):7-22. [DOI:10.29252/ijn.32.117.7]
20. Abolhasani F, Bastani F. Successful ageing in the dimensions of life satisfaction and perception of ageing in the Iranian elderly adults referring to the health center in the West of Tehran, Iran. Iran Journal of Nursing. 2019; 31(116):61-74. [DOI:10.29252/ijn.31.116.61]
21. Mohammadpour A, Sadeghmoghadam L, Shareinia H, Jahani S, Amiri F. Investigating the role of perception of aging and associated factors in death anxiety among the elderly. Clinical Interventions in Aging. 2018; 13:405-10. [DOI:10.2147/CIA.S150697] [PMID] [PMCID]