I'm about 35 years past my prime (I was a late starter). Apart from sights and sounds, here are the things I enjoy:
-- having a goal, figuring out how to train for it, doing the training, and meeting the goal
-- even though my speed at my engine's redline is increasingly slow, I love knowing that I understand where the redline is and can stay there for a long time
-- doing something that's fairly difficult, such as a 45 mile fast walk with a 6000' climb, staying at my redline, not getting into trouble, and having not a damn thing left in the tank when I finish
-- maybe once a year I grab a M70+ award, which feels good, even though there's a very small pool of M70 guys on my island.