Research suggests that physical activity may influence sleep, yet more research is needed before it can be considered a frontline treatment for insomnia. Less is known about how this relationship is moderated by age. Using multilevel modeling, we examined self-reported physical activity and insomnia symptoms in 18,078 respondents from the U.S. nationally representative Health and Retirement Study (2004–2014). The mean baseline age was 64.7 years, with 53.9% female. Individuals who reported more physical activity (B = −0.005, p < .001) had fewer insomnia symptoms. Over 10 years, the respondents reported fewer insomnia symptoms at times when they reported more physical activity than was average for them (B = −0.003, p < .001). Age moderated this relationship (B = 0.0002, p < .01). Although modest, these findings concur with the literature, suggesting moderate benefits of physical activity for sleep in older adults. Future research should aim to further elucidate this relationship among adults at advanced ages.