There was an article in New Scientist ages ago where they were examining a group of nuns who never got alzheimers, despite living for ages.
They were investigating dietary/alcohol/drugs under the presumption that the clean living of the nuns might be protecting their brains.
Were shocked when they did brain scans, and found swiss cheese in intelligent lucid women.
The difference was that they had no idjit box and spent their time reading, doing crosswords in groups, playing board games and doing craft.
The premise was that the continued exercise of the brain will build paths around damaged areas.
I haven't known too many old guys in a fully equipped shed to degrade into babbling dribblers (become eccentric certainly, but still able to reason, build etc.), but have known quite a few "retirees" develop vegetative states.