What I am about to say worked for me and it may work for you as well. The key, I think, is starting something new every 5 orso years after you leave your chosen endeavor. But, and this is the really big but, it has to be something you've never done and even a bit scared or intimidated to try. Why something you've never done? Easy answer - because you can't get worse at it. If you've never done it beforeyou can only get bettrer at it by doing it. Every small step is growth. I was given the opportunity to be studio photogrpher at the Jane Pauley Show for one day. The picture of Jane and the Metallica crew was printed in Variety, People, the Star and Rolling Stone magazines.
And the real key is when you get good at doing something in older age is to stop. You don't have to be excellent at it, be satisfied with good and start something new. Golf is an excellent example, playing golf every couple of days at age 70 is not going to lead to a professional career, but can lead to frustration in the search for excellence. Be satisfied with good and just enjoy the game, but also try something new.
I retired from dentistry at age 61, I had reached a point of being really excellent at what I did and I did not want my abilities to decline over the coming years. I had accomplished what I had set out to do - I had a good practice, taught at a prestigious dental school, authored a textbook, lectures in the United States and abroad. It was time to go. I went on to create web sites commercially, ran a large directory site for dentists, worked as a studio photographer, hosted a radio call-in show and now created a podcast.
It worked for me, it might for you as well.