I'm a bit overweight, Senoufou, but for my age (62) I'm pretty fit, I think. I do British Military Fitness 4 times a week, and usually get in a couple of 10 km runs and a bit of rock climbing on top of that (and ice climbing in winter).
I do half marathons in just over the 2 hour mark these days, but hope to get back under that before the end of the year. I generally do 4-5 a year. I've recently taken up Endurance Marches, which are all-day events (sometimes 2-3 days).
I failed miserably on my last one, though (36 km over pathless bogs in the Brecon Beacons carrying a 50 lb pack and a scaffolding pole, in the wind, rain and low visibility). I gave up after about 13 km, as I was going far too slowly to make the cut-off time for successful completion. If you're interested in what these involve, see: IronMan Blog . I'm NOT the Rob mentioned in that Blog, as I gave up at RV 3 on my own attempt!
Still, however wet, cold and miserable I got on that one, I'd do it again in a heartbeat rather than watch a couple of youngsters getting married on TV! :-)