I'm 51, never raced in college, and took a long time off after age 19 (until 46). I'm decent, but not exceptional.
HS 1/2, mile, 2 PB's: 2:04, 4:34, 9:42 (1977)
800, 1500m: 2:21, 4:40 (2010)
(the 1500 translates to about a 5-flat mile for comparison)
Post High-school road 10k PB's:
33:20 (1979)
35:51 (2010)
I train much better now than I did at 19 when I ran my 10k PB. These days, I do about 45-55 MPW, with a couple of harder workouts each week....still much room for improvement.
I don't have other direct comparisons, because oddly, I've hardly ever run the same distances as I did back then. Most distances were in miles, and they never had road 5k's....that was considered too short. At longer distances, I have from 1979 a 56:15 (10-mile) and 1:58:09 (20-mile), to compare to a 2009 half-marathon of 1:20:11.
Your heart slows down as you get older, not much can be done about that, but you should address your aches and pains. I'll bet you'll get faster when you do.