All parts of the body eventually go old/bad, so I don't see why the brain would be different. Prevention? No. Delay? Possible.
I read an interesting article recently that studied why people in professions that are generally thought of as requiring a high level of intellect, i.e. professors, doctors...appear to as a group delay dementia compared to the general population. The depressing result was they don't, they basically suffer cognitive decline at the same rate as everyone. However, because they started at a higher cognitive level, it takes longer before the decline shows up positive on cognitive decline test compared to the average person who's operating closer to that line their whole life. So sometimes the delay isn't even real, if you're a brilliant physicist it's probably nearly as depressing to think about declining to baseline as it is to think about going the rest of the way.