Generally, nothing that's not fun is worth pursuing. And, if something isn't fun, it's also very likely it is something that will never be excelled in.
If you play only for the rating and your rating isn't going anywhere, then maybe it is time to leave chess behind. If, however, you can forget about ratings and get back to the simple joy of the game, then maybe it's worth staying with a slightly adjusted perspective. Good luck either way.
I'm 64. I didn't pass 2000 until I was in my early 60s.
Maybe you just haven't peaked yet?
That's inspiring! I would love to pass 2000. May I ask how you got there?
Never had a trainer. But if I had to recommend a couple of chess books that changed my way of looking at the game, they would be "My System" by Nimzovich and (especially) "Pawn Power in Chess" by Kmoch.
Other than that... play slow games. Analyze them afterward. Study games by the old masters (from before the computer era). Study tactics, model mates and typical endgames. Learn the typical central Pawn formations and their effect on middle-game planning.
Players nowadays spend far too much effort memorizing openings, when middle-games and endgames would benefit them more.