Well you were arguing against Keegan but painting a picture on the entirety of the NBA, and while I have no specific metric to point at for this because I don't know where it would exist, I can say unequivocally human being can get quicker and faster through their 20s.
The most prevalent I'd say is Usain Bolt
He consistently improved his times from age 21 through age 27
https://www.thespeedproject.com/athletes/usain-bolt/
But just go look at Track athletes times from freshman in College to Senior in College, then those who go on, look at them progress as they get into worlds and Olympics.