If you find that you are declining mentally after 30 or 40, you are either doing something wrong or are genetically extremely unlucky.
Exercise, a good diet, proper sleep, combined with plenty of intellectual and social interactions seem to be enough to keep you from measurably losing any mental faculties well into your 70s or 80s (and even 90+ if genetically lucky).
It actually is inevitable, as even you admit when we begin to reach our 70s/80s ;). If we don't die of something else, all of us will die of Alzheimer's. Simple fact of universal amyloid plaque buildup. http://www.amazon.com/Ending-Aging-Rejuvenation-Breakthrough...
Also technically incorrect on the mental decline as well - our brains do start to irrevocably decline at around age 30. Our myelin sheaths fully develop in the early 20s, and from there, we have a few golden years until it's all downhill :D http://www.sciencedaily.com/releases/2009/03/090320092111.ht...
If you find that you are declining mentally after 30 or 40, you are either doing something wrong or are genetically extremely unlucky.
Exercise, a good diet, proper sleep, combined with plenty of intellectual and social interactions seem to be enough to keep you from measurably losing any mental faculties well into your 70s or 80s (and even 90+ if genetically lucky).