22 for me.

When I was around 22 I was in the best shape of my life. Assuming that the prompt means going back to the same state, I’d take it with no hesitation. It was before I damaged both my shoulders and started putting on weight, and it was before the chronic illness I have had shown itself and caused a lot more problems for me.

If it means that my body is reverted and not my mind, I could go to see my doctor and make sure that none of the damage happens, and be in a much better condition than I am now.