I'm 57 and I started running this year. Overtraining is the biggest issue for me. I'm up to about three miles maybe four times per week, but most of those miles are zone 2 HR, really slow and easy runs. On the weekend I'll do a tempo run, or intervals, alternately. If I maintain that schedule for more than a month or so I end up a little more sore every time I go running and my time starts to drop. So I have to take most of the week off every four or six weeks. I also take a lot of supplements; creatine, L-carnitine, Beta-Alanine, protein, etc. They help. I feel I can exert myself more since I started taking them. I also take EFAs for joint health, collagen for connective tissue recovery, and sometimes MSM, though evidence on that one is spotty.