like GOBNU, i'm 49 (although female) and have been in stress fracture mode, but i hope to resume running in a week (it will have been 10 weeks since the injury -- this is my fourth running-related SF). a couple of tips to you.
first, be very very cautious as you start back. the first week: on smooth grass: 3 min run, 1 min walk; repeat for a total of three of these, all the time monitoring how the site of the injury feels. if it's okay, do this every other day for the week. if it's still good after that -- as in not only no pain, but no awareness of the SF area -- then you're ready to start wisely increasing mileage. (i tried this at 8 weeks, and the second rep of the first day made it clear that i needed to wait a while longer.)
second, hills are good because there's less pounding (going up), but if you can do your mile repeats (by either distance or time -- a GPS is useful here) on grass instead either road or track, that's best. soft, natural surfaces are good. in fact, the more you can do on dirt or smooth grass the better.
i agree with JoeGarland regarding respecting new discomforts -- and managing all the familiar ones.
finally, to counteract all the doom and gloom of getting older, i should mention that after each of my couple-of-months-long layoffs, i've come back with PRs: three years ago after a SF, i PR'd in the HM, then after last summer's hamstring-induced layoff i PR'd in the 5K and 10K; in between i broke 8 hrs for 50 miles (trails). while not running, i've spent lots of time rolling around the countryside on my bike.