Any muscle not used becomes stagnant. Our brains, being one of the most largest and the most essential, will decay if not put into active activity as we age. The key becomes to maximize our brain activity as much as possible for ultimate longevity.
The best possible way to do so, is by keeping our minds functional and engaged during our leisure time.
This by doing “think” provoking activities we enjoy doing. The ones which challenges us while being fun, so we’ll want to participate and do them often.