Time to Experiment

I've been reading thousands of pages of research on aging runners and have been finding that there's almost nothing addressing the sub-populations: there are those who take up the sport later in life, there are those who competed in college and then took 20 years off before returning, there are those who got by on minimal training and competed continuously and there are those who ran themselves into the ground (like me) through decades of high mileage and heavy racing schedules.

I want to know what the differences are between runners like myself and those who are cleaning up in master races (who are all in the lower lifetime mileage groups) and whether those differences can be eliminated. There are vague references to decreased elasticity of tissue being the major problem - and given that my achilles tendons are now just calcified scar tissue, this seems a likely candidate. Can this be overcome?

There are numerous possibilities for what is lacking and I think I can find simple reliable tests to measure them. I'm thinking that simply repeating the tests regularly should improve the measurements and should lead to improvement. If there is something that can't be improved and correlates with failure to improve in running, then I'll know it's hopeless to make a comeback. I sincerely doubt such a thing exists, but I do think it quite possible I'll end up get injured doing the tests, which would leave me both hurt and wondering.

Here's the tests.
1) Flexibility: v-sit and stretch. Seated with yardstick between legs, reach forward to see how far beyond heels I can reach.

2) Balance and propioception: Timed one-legged stand with eyes closed.

3) Static leg endurance: squat to 90 degrees with back against wall and hold for time.

4) Vertical leap for height.

5) Standing broad jump.

[Three for a football field:]

6) 25 yard hop, trying for as few hops as possible.

7) shuttle run: 10 yards, back-and-forth, twice, for time.

8) 40 yd. sprint.