Friends have been forwarding this article: http://trainright.com/5-best-habits-athletes-over-40/ and, of course, I don't agree with it. Parts of it are correct for most people, which is true of just about everything. Athletes don't need more protein, older people don't need more protein; if you're getting 15% of your calories from protein (up to 20% if vegan), you're getting all you need and more just increases your cancer risk.
Here's some things I've learned about running when over 50:
1) Don't do the races your friends think you should want to do.
What you enjoy most, what you do best and what you do most should be the same thing. If you're running the Boston Marathon because every time a co-worker hears you're a runner they ask if you've run Boston - and you're a sprinter - something's wrong.
2) Rest better.
Rest more, sure, but rest better as well. You can still run hard workouts, but you'll need more days between them than you did in your 20's. I used to follow a day of 800m repeats in 2:25 with a 24 miler under 3 hours, because I couldn't run fast that second day - but it was, of course, a hard day, just "hard" in a different way. Take at least one day off per week, but be wary of masters programs that are only 3-4 days per week. The days you don't run can be devoted to:
3) Do all the preventative maintenance stuff you've neglected.
When I was in college, I had a coach that had us doing calisthenics that he was better at at age 70 than I was at 20. But I didn't need to do those things; I felt my time was better spent either running or doing nothing. Now, at 50, I have a million imbalances and weaknesses that could've been prevented and I do all the therapy exercises for rehabilitating old injuries every day; essentially, I'm doing the same exercises my 70 year-old coach was doing that he learned the same way I did.
4) Ignore the hype of the new.
Whether its Cordyceps, propioceptor neuromuscular facilitation or shoes with some "revolutionary" design, if you haven't needed it thus far, it probably isn't going to make much difference. "Runner's World" has survived for 50 years on finding new fads to promote because what you really need to know wouldn't fill one issue.
5) Know that no one will heed your advice.
Sure, you've had the same injury as your friend now has and you found a way to recover, but they're not going to listen. Yes, you've done the race they're training for, but it was a long time ago and that somehow negates it. That guy running faster than you, whose only been running for 6 months - now he must have the answer, because... he's faster than you.
You'll get used to it, once you remember that you were the same way once.