I'm 67, in pretty good health and active - 150+ minutes of moderate exercise a week (mostly walking and swimming). Why am I trying C25K? Two reasons. Firstly because the evidence suggests that a bit of vigorous exercise brings further benefits. Second because I'm told that running makes you feel good, and I won't know until I've tried. Well, I'm now on week 4 and feel no benefit. Just rubbish during the run and immediately after - and that's it. I read posts by people who say they feel SO much better even after week 1, so why don't I? I'll keep going but I can't envisage ever liking it!