Most people's bodies are at their 'peak' when they are in their early-to-mid 20s. After that, the body starts to go 'downhill'. They put on a few pounds every year, start to develop aches in their back or knees, have less tolerance for exercise and other physical activity, start needing reading glasses. The aging process can wear a body down. However, if someone finds a solution, such as diet, exercise, vitamin supplements, yoga, hormone shots, etc, then they might feel better, like they did when they were younger. That's when they would say, "I feel like I have my old body back."