I'm 44 years old. I am in better shape than most of my peers and people always estimate that I'm younger.
Larry, you're 44?!? Chalk me up as one that thought you were younger....by at least 6-8 years (based on the age of your kids). As for better shape than most of your peers, most of the 40+'s (you know...the OLD guys) on the board are in better shape than 99% of the people 20+ years younger than them....that's impressive.
Andrew, running on concrete is a lot of impact to your knees and ankles.
As for the original question, I'm not sure of the answer. But I'd rather be 60 with bad knees and great health than 60 with good knees and bad health.