We have a 22 yo gelding. He doesn't have any major issues apart from a little arthritis which we treat with NSAIDs. With light work he shows no symptoms of arthritis. He is a little harder to keep weight on than our younger horses but we just make sure he is rugged whenever its cold and that he has full-time access to good quality hay.
When I bestride him, I soar, I am a hawk: he trots the air; the earth sings when he touches it; the basest horn of his hoof is more musical than the pipe of Hermes. ~William Shakespeare