I'm 74 and have been playing again for about 7-8 years. I first played in the bar scene from 1970 - about 1983 then quit for 30 plus years. After taking it back up I was somewhat stagnant in my playing for 4 or 5 years but have now been progressing in ability every year.
Looking at my league average, I was about 10% better last year than the year before, and this year 3-4% better than last year. I feel it is still possible to improve maybe 10% or so but it gets tougher as the years go by.
Shooting two leagues has helped somewhat, but realizing what problems I can reasonably work on has helped more. I try not to dwell on more than a couple things at once in practice. Also, I have other interests and while I could shoot with friends for a couple hours or so, I can only stand to practice by myself a half hr or so at a time.
Sadly, one issue has popped up these last couple years and that is some occasional shaking in both hands. If it starts on pool league night, it's not going to be a good night. You can still somewhat shoot through it, but it really affects softer finesse shooting. I even have it at home now and then and will just walk away and come back in a couple hrs to try again. I actually can tell ahead of times if it's going to be a problem as my fingertips almost feel as there is electric current going through them. Anyway, it's what it is, but if it gets much worse, I may consider at some point quitting, but that's something for down the road as for now I still am improving.