Your muscles atrophy if you don't use them. A 60 year old power lifter is stronger than a 30 year old who never lifts. On average people lose around 5% of their

Your muscles atrophy if you don't use them. A 60 year old power lifter is stronger than a 30 year old who never lifts. On average people lose around 5% of their muscle mass per decade after 30; someone with twice as much muscle mass at 30 is still going to have more muscle mass at 60 than the person who started at 30 with half as much muscle mass.