Remember this Motherfuckers! (I just wanted to cuss):
At a very deep (if abstract) level your brain is just another bunch of muscles.
Fitness and health addicts: keep yourselves mentally challenged.
Exposure yourself to new ideas, talk about things you don't understand, work on puzzles that are difficult.
Do that and keep up your cardiovascular health and you can hold on to (even improve) your mind in your twilight years!