Excellent post. I also bike ride, but at 75 my physical activities are limited. I read for 3 hours a day which is quite mentally stimulating, plus routine home and personal maintenance means learning new ways of coping.
I would add that seeking out new music is a creative exercise that stimulates the brain. In the past year, I've started listening to music I never liked before. Not forcing myself to like it, just allowing my brain time to appreciate what I'm hearing. That's led to going out for new musical experiences, learning about music history, and understanding different ways of connecting.

