Background: A questionnaire assessing awareness of positive and negative age-related changes (AARC gains and losses) was developed in the US and Germany. We validated the short form of the measure (AARC-10 SF) and the cognitive functioning subscale from the 50-item version of the AARC (AARC-50) questionnaire in the UK population aged 50 and over. Methods: Data from 9,410 participants (Mean (SD) age= 65.9 (7.1)) in the PROTECT cohort were used to explore and confirm the psychometric properties of the AARC measures including: validity of the factor structure; reliability; measurement invariance across males and females and across individuals with and without a university degree; and convergent validity with measures of self-perception of aging and mental, physical, and cognitive health. We also explored the relationship between demographic variables and AARC. Results: We confirmed the two-factor structure (gains and losses) of the AARC-10 SF and the AARC-50 cognitive functioning subscale. Both scales showed good reliability. Convergent validity was good for AARC losses, but weaker for AARC gains. The meaning of AARC gains and losses was the same across males and females and across individuals with and without a university degree. Items in the AARC scales had the same meaning across individuals with and without a university degree. Items in the AARC-50 cognitive functioning subscale had the same meaning across males and females. Single items in the AARC-10 SF had different meaning across males and females. Demographic variables predicted AARC gains and losses. Conclusions: The AARC-10 SF and AARC-50 cognitive functioning subscale can help to identify UK individuals who perceive age-related changes in their mental, physical, and cognitive health.