Here's some food for thought

What if most people didn't suffer a loss of mental acuity as they aged? Say, someone is 90 years old but has a very good memory and doesn't have any problems with mental fogginess or forgetfulness.

I know most of the effects of something like this would be beneficial, and positive. But what would the negative effects be? I've got some ideas, but think about it and let me know what yours are. It's for something I may do in the future . . . this is your chance to contribute! Heh.