The healthiness of one's brain can pretty well be judged by whether one embraces the uncertainties in life with pleasure.
A kid has great expectations for the future. On the night before the school trip, for example, it is not uncommon for a kid to be so excited that it is difficult to sleep. It is not that those school outings are going to be anything great in actuality. It is just the expectations that brings the children into the cosmos of the infinities.
As one grows older, this great ability of being excited over the unknown is gradually lost. The future becomes mundane. There, the decline of the brain health starts.
Looking forward to the unknown, no matter how small it might be, is a great way to keep your brain young and up.