I'm also in "comeback" mode after a 25+ year layoff (wow, most letsrun posters aren't even as old as my layoff!!). I'm 47 now.
I would love to believe that my legs are somehow "fresher" than my non-quitting friends but the sad fact is that they regularly kick my butt (These are people I used to beat back "in the day" even off of very little training) Of course, it's taking me longer now to get back in shape and I think I will have to do much more mileage. I don't think I can "get away" with less now.
Having lots of friends who have continued running makes me fairly skeptical of this late starter "freshness" hypothesis. There are so many variables to consider and control for.
For one, lets not forget the fact that many non-runners develop joint problems, leg issues, heart problems etc. as they age. There also seems to be a genetic component that can't be dismissed. Some people just deteriorate at a faster rate when they get older, running or not.
Case in point: I have a friend who ran a lot non-stop since high school, including several marathons. He has recently developed arthritis in his mid forties. Ah ha!! you say? There's proof that the continuous pounding screws you up, right? Well, not so fast. You see, he has a twin brother who almost never ran and developed the SAME problem in his 30's. So, you could argue that perhaps the running gave my friend an extra 10 years, and even now, he's still not as bad off as his brother.
Also, the late starters who do well are probably not in the group who deteriorate so fast as they age. People with arthritis, knee problems, etc in their forties are probably NOT going to start training seriously. So we have a selection bias. Furthermore, what about all the late starters or returnees who "suck"? We just don't hear about them.
The best way to test this "freshness" hypothesis and control for other factors (like genetics) would be to round up a large sample of twins and have some of them run continuously since high school to mid forties. Then have a group run in HS/college and take time off to forty and start training until 45. Have a final group not do any training until 40. Of course, such a study is probably impossible to do so we are all left with stories like the one of my friend that I mentioned above.