This is a really striking way to present the data, nice work.
Putting this in perspective, I started running as a college freshman in 1990 and had my best success as an open athlete as a college senior in 1994. I came back as a masters runner and have been steadily at it for about 7-8 years. My best age grade percentages from my times in the mid 90s (spanning from the 3000m through the 10,000m) and my best age grade percentages as a masters runner (spanning from the 5000m through the marathon) - a stretch spanning over 25 years - are all within about 4 percentage points, with no material improvement or decline in age grade percentages over time.
Thanks! I stole some of the data from one of Derek's articles then added the age graded info and sorted it descending. You are 100% right, you get all your improvement and highest scores when you start running, or are young. Fran's trajectory is completely fantastical!
Of course, you have ignorant runners who will claim, "I started running when I was 50, ran a 4:30 marathon, and then improved to 3 hours over the next 10 year" and try to use this to claim that Frank's time could be legit. But what they don't realize is they are going from the 70% range to the 80% range! You don't go from 75% to 95% in your 60's after you have been running all your life!