Happy birthday, OP. I'm about to turn 54 and also feel the age difference these days. Mostly in my world view of things. Sigh.
But things I have done that make me feel 15 years younger:
1) much better fitness regimen. I haven't felt this good physically in years. Kick yours up a notch and feel the benefits.
2) I have been taking data analytics classes to increase my professional skill set. Not only does it make me more valuable to my organization, but the mental work involved really makes me feel smarter. Pushing yourself in an area that you aren't used to is great for the brain.