I am "only" 58 but I believe there are a few factors.
- your micro-movements are somewhat trembling (I realise this much more in another hobby of mine which has to do with microscopes - it is much harder for me now to move objects under magnification by hand)
- your eyesight is not as good (look at really small script on coins etc. - there are some instances where you can't read stuff without a magnifying glass and on the other hand you are not able to see as well in the distance, too.
- as RKC already said, focus is lost sooner. I know that I can stay focussed for short periods but if I play longer sets, I start losing it
I think that other hobbies like microscope work or scale modelling etc. are a lot better to identify these weaknesses aquired with older age. In pool, it is a bit hard to see why you miss a certain ball.
I find that I just don't have the drive to practice fundamentals like I did 25 years ago when I was in my 40s. Ronnie O'Sullivan, still a Top snooker player AT OVER 40 pots 2000 plus balls per week in practice. How many of us even do disciplined drills for an hour a day, 5 days a week? I can barely manage 30 minutes 3 x a week and being retired I have the time.