The aim of this study was to describe and systematically evaluate the psychometric properties of attitudes to aging measures that have been validated in adults younger than 60 years. Studies were assessed for methodological quality using the COnsensus-based Standards for the selection of health Measurement INstruments. Best evidence synthesis was performed to summarize the levels of evidence. Systematic searching yielded 21 articles, relating to 10 different measures. Some instruments were validated only in middle-aged and older people, while others were validated in a wider age range. Measures differed in whether their items related to participants' own experiences of aging, their anticipated future aging, and/or aging in general. None of the measures had had all of its psychometric properties assessed. The Expectations Regarding Ageing-12 and the Anxiety About Ageing Scale received positive ratings for the greatest number of psychometric properties, but capture different constructs, and may be differentially suited to different age groups of younger adults.