This study analysed the relationship between age and items of the Work Ability Index (WAI) among 19‐ to 62‐year‐old female home care workers (n = 636). The first significant decrease in work ability occurred between the ages of 40 and 44 years, and a second, sharper decrease occurred after 55 years of age. The subjects' physical work ability deteriorated as early as 35 years of age. In addition, current work ability, number of diagnosed diseases and work impairment due to diseases proved to be the most age‐sensitive measures of work ability. The subjects who perceived their health status as poor had the highest risk for poor work ability. Moreover, the age‐adjusted odds ratio indicated that the WAI was strongly associated with age and musculoskeletal and psychosomatic symptoms. Ergonomics, possibilities to control one's own work, time pressure and management were the features of work that predicted work ability. The study demonstrated the need to promote the work ability of home care workers early in working life. Among both older and younger workers, preventive measures should focus on the above‐mentioned factors.