I am held back at this point by age. It's a case of "If I knew then what I know now." I was a very good local runner in the late 70's/early 80s, but trained way too hard and spent a lot of time injured and frustrated, despite excellent advice from many quarters. Now that I'm in my 60s, I have time to train and the patience and knowledge to do it right. Therefore, my "age graded" results are much better than in my youth.
The lesson for you young guns out there is that you need to be smart now, not later. Genetics will limit you in the end, but if you eat, sleep, and run properly, you can maximize your potential and not find yourself wallowing in regret and crying bitter tears. "I coulda been a contenda!"
Did I say that out loud?