Intellectual enrichment is good for the brain. Educated people who make novelty a way of life and continue learning age well. The key to good cognitive function at any age is novelty. There is part of the brain that is built to detect novelty and alert the rest of the brain. With that alerting comes neuritic growth and new circuit.
Novelties can be new sports, painting, sculpturing, music, chess and being seriously in love.
A healthy brain needs continuous mental and physical stimulation and new challenges. When you retire you need to start new challenges if you want to prevent retraction of neurites. It is not only the question of being smart. A brain with large numbers of connections seems to help the owner. It seems the brain can decide his own destiny when it has a lot of connection.