Abstract Background Frailty can occur in older adults without disability or multimorbidity. Current methods focus on the most frail, but poorly discriminate among those “not frail.” Methods The Study of Muscle, Mobility, and Aging (SOMMA) included 879 adults aged 70 years and older without mobility disability. We operationalized frailty domains using: peak oxygen consumption (endurance), digit symbol substitution test (speed), leg power (strength), perceived fatigability, D3 creatine dilution (sarcopenia), and accelerometry (sedentary behavior) to construct a frailty score of 0–12 summing tertiles (0–2) of each component. We used linear or logistic regression with and without adjustment for confounders to examine associations with age, reported, and performance function. Results The SOMMA frailty score distribution was broad and strongly associated with age (r = 0.33, p < .0001). Each point was associated with a 30%–50% higher odds of having reported difficulty with activities of daily living or mobility. After grouping the total score (0–3, 4–7, and 8–12) those in the highest group were 9–31 times more likely to have functional limitation, and at least 8 times more likely to have poorer function after full adjustment. Higher scores identified those less likely to report ease of walking or higher physical activity. Peak oxygen consumption, leg power, fatigability, and digit symbol score contributed most to these associations. Conclusions The SOMMA frailty score characterizes frailty as a continuum from frail to vigorous with assessments that are amenable to change. Associations with age and function suggest utility for distinguishing a wide range of vigor and vulnerability in relatively well-functioning older adults.