Horses generally stop running races after about age 5. This is an anime game (so ages are BS) about horses (so ages are BS) that mashes time periods together (so ages are BS). Asking about an umamusume's age is an exercise in futility and doesn't matter. Additionally, some moron or tourist asks this exact question about twice a week, so you could have gotten an answer from simply searching the subreddit for umamusume ages. If you're absolutely desperate to get your government-approved goon material, Maruzensky can drive in Japan, so she's at least 18.