I'm 27, but I know plenty of people in their 50s who can run further than I can. One guy I know is in his late 40s or early 50s, just had knee surgery (sometime between now and February of this year) and is back up to 9 miles. I've never run 9 miles! In fact, if I'm honest, I couldn't run a mile October 1st 2009, but over the last six months I've corrected that. I'm still over weight and could certainly be in better shape, but at some point I said to myself that all the gear in the world is not going to help if I can't move a mile on foot.

I just pick five as a base level because it is an achievable goal at which point I think that if you just allow yourself to walk you could go a lot further in a pinch.

Also, my mother is in her 50s and through a lot of self determination and a little bit of encouragement from me she can now run over 3 miles!

Point being, I don't think age has to be a factor. Now if you're disabled, that's different, and probably unfortunate for you in a bad situation. If you're just lazy and/or fat, I have little sympathy for you, particularly because I'm fat I'm just a little less lazy than I was six months ago.