Are you a female? Don't worry, females don't accidentally become muscular. Heavy weights and adding muscle to your body won't make you "muscular." We don't have enough testosterone for that. You'll just look slimmer and fit. It takes a concerted effort for females to become muscular, and sometimes even supplementation. Especially at age 60, it's almost a guarantee that you wouldn't become "muscular," certainly not unless you were intentional about it.