The brain training via crosswords, etc., is important and I do them too. But now my 81 year old mother, about to have knee replacement surgery, tells me PHYSICAL ACTIVITY - as in walking, swimming, biking, etc. is also crucially important to keeping the brain unfogged and active. (She's been taking classes as well as exercising daily for some time now.)
Boomer in Chief of Boomer Women Speak and the National Association of Baby Boomer Women.