A Systematic Review Toward a Comprehensive Framework for Measuring Non-chronological Age

Abstract

As populations age globally, there is a need to refine the understanding of aging beyond simply chronological age. Therefore, this study used the PRISMA framework to synthesize literature on alternative aging metrics beyond chronological age. We analyzed articles from 6 databases (SCOPUS, PsychINFO, Web of Science, CINAHL, Engineering Village, and PubMed) and selected 18 articles that explored factors that lead to older adults’ individual differences. Findings indicated the necessity of a consistent terminology that better describes one’s cognitive and physical functioning, such as “non-chronological age.” Also, the review found that daily cognitive, physical, and social activities may result in different non-chronological ages. A comprehensive tool to measure non-chronological age and thereby provide a more accurate representation of aging that incorporates these critical factors is needed. The findings may contribute to the development of theories in non-chronological age.

The population of older adults is increasing. The number of Americans aged 65 and older is projected to increase from 58 million in 2022 to 82 million by 2050, which represents a 47% increase (Mather & Scommegna, 2024). This trend suggests a substantial and continuing increase in the older adult population.

As people age, they may experience various physical and cognitive declines that can significantly impact their daily activities. Multiple factors influence how bodies and minds function. Chronological age, the number of years an individual has lived, may not be the best predictor of task performance. Lifestyle, cognitive and physical activities, and social networks, support, or activities may also play a significant role. Therefore, it is crucial to consider various variables beyond just age when predicting one’s capabilities (e.g., Huang et al., 2022).

The goal of this study was to systematically synthesize research on non-chronological age and factors contributing to individual differences among older adults. We aimed to provide insights into building a framework to redefine aging using a “non-chronological age” approach.

The Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) method (Moher et al., 2009) was used to identify relevant research articles. Six databases were searched: SCOPUS, PsychINFO, Web of Science, CINAHL Complete, Engineering Village, and PubMed. The initial research was performed in November 2023, and all the databases were last accessed in December 2023. Only journal articles published in the English language were considered, and the search included studies published between the years of 2000 and 2024. Keywords related to non-chronological age (e.g., non-chronological age, felt age, and successful age), older adults (e.g., older adults, elderly, and seniors), and daily activities (e.g., daily life, and instrumental activity of daily living) were used for the search. Overall, 18 articles were included in the final review.

Findings revealed that there was no universally accepted term for the concept of non-chronological age. Terms such as “non-chronological age” (Huang et al., 2022), “felt age” (Choi et al., 2021), “optimal age” (McReynolds & Rossen, 2004), or “successful age” (Jopp et al., 2015), were used interchangeably. This indicates a need to establish a standardized terminology to better understand non-chronological age.

Among all the papers, three main categories of factors that may affect non-chronological age were identified: physical, cognitive, and social. Physical activity or exercise contributes significantly to non-chronological age, as it enhances muscle function, flexibility, cardiovascular health, mood, and cognition, helping individuals “feel younger” than their chronological age (Choi et al., 2021; McReynolds & Rossen, 2004). Cognitive factors involve engagement in various activities (e.g., reading, creative pursuits, outdoor activities) that help maintain cognitive health and prevent diseases such as dementia or mild cognitive impairments (MCI) related to cognitive decline (McReynolds & Rossen, 2004), resulting in better non-chronological age. Similarly, social factors, including social networks, social support, and social activities, also play a significant role in developing a better non-chronological age. Participants who were more socially engaged, such as engaging with communities, volunteering, or continuing participation in the workforce even after retirement, demonstrate greater cognitive ability and, thus, a younger felt age (McReynolds & Rossen, 2004). Education, socioeconomic status, mental health, and a nutrient-rich diet are also significant factors influencing non-chronological age (Borgeest et al., 2020; Lauenroth et al., 2016).

The findings of this study may inform the development of a framework that redefines aging using a non-chronological age approach. For example, a model that includes physical, cognitive, and social factors may help create personalized interventions or assistive technologies to improve the quality of life for older adults.