In reply to mypyrex:
1 hour 40 is a decent time for a HM, and if you could do 10 miles a night 6 days a week, you must have had the motivation thing taped. That's very hard to do once, never mind for long. By which I mean that a tiny minority of runners I know of or am aware of manage that.
Trangia's comment about the age specifics of joints and bones is important, but having made the decision to run, and wondering how best to do it such that you keep going, that depends on you. If you have sufficient self motivation, just go out and do it. Vary your routes for interest. To start with, don't bother timing yourself. Just do it and rediscover the hang of getting out there. If you want to stop, stop. I do! Once you are into it, get a GPS watch, or use your phone, register with some site like Strava and log your routes. I have found that very cleverly constructed site to be astonishingly motivating. But do what works for you.
If you are a social animal, then join a club and get out with them. I'd find that very constricting, but clearly very many people find this an enjoyable and motivational way to keep on doing it.
Don't try to do 10 miles a night! When I had a motivational lapse a couple of years ago, I found that it was very helpful to set the bar very low, never mind where once it had been. The main thing was to get going each day.
And if you can't run, remember that you are a mere yoof compared to a guy called Reg that I have met many times on the Camel trail near where I live. He is well into his eighties and was one of the commandos who opened up Sennen. He knew Joe Barry and Mike Banks, I think. Every day, without fail, he walks six miles on the trail. First day this way, next day that way. I hope I can do that at his age.
Edit: Reg, not Ron.
Post edited at 18:00