The unfortunate truth is that as we age after around 30 years old, we begin to lose muscle mass. You can still gain muscle mass if you train for it fairly well after 30, but the effectiveness begins to decline the older we get. And if you are consistent in training, over all strength can still be maintained for quite some time. But some research suggests that the remaining muscle mass and biomechanics are integrating to maintain the strength. Non exercisers will almost all experience significant muscle loss as they age if they do not begin an exercise program.