Regular weight lifting has been shown to improve muscle mass in people of all ages. Even ninety-year-old participants in weight-lifting studies benefited by supplementing their muscle mass.
It can be inferred from the above passage that
Explanation
The first sentence states that people of all ages can benefit from regular weight lifting. Furthermore, the selection cites the example of ninety-year-old participants who saw improvements in muscle mass. Thus, it can be inferred that you can start lifting weights at any age and see improvements.