I would give anything to be 40 again, oh wait most people think I'm younger than that!
Seriously, it's all mental, discipline and moderation. I'm your hobby jogger not someone who was ever "fast" but I like to keep in shape. Lately, I don't have motivation to run consistently or even train--partly due to life changes, job etc but i always find time to workout whether it be hand weights and running up &down stairs at home, going to the gym (do elliptical, spin, run, machine weights) or running/hiking outdoors (although too warm by the time I get home from work now). Even if it's only for 30-40mins at a time.
The key is wanting to feel good about yourself and mine is through exercise, moderation in food/drinks, drink lots of water, laugh at yourself and meditate (right before bed listen to soft music and read). Keeping mind and body at a balance will help make you feel and look younger. Don't dwell on the wouldas, shouldas and couldas.