The body does age at a different rate than the mind.
The above is something I am absolutely, positively certain of, period. At age 45 I think I am finally (well over the past few years) started to become mentally mature. Of course there are times when I think my body is aging far too fast, but then I remember that there are times in the past when the average life expectancy was something like 45, so the issues I have seem minor in comparison.
It is all so very, very cruel in a lot of ways: We are given this physical hardware but when it is at peak efficiency (when we are in our, say early 20's) the software we have inside our heads isn't powerful enough to run it right. How's that one for a geek analogy?
There are ways of dealing with this stuff. I can make the choice to eat healthier. I can choose to exercise more. It's all about what you want I suppose. I want to be very active in my older years. I don't want to be some person who sits in front of a TV screen day after day after day, waiting for the next CSI re-run and ultimately just waiting to die. I know, we all die in the end. Well we all do die, it's just that we don't - and shouldn't - spend all of our time thinking about that constantly. That would be a waste of life.
Maybe the trick in life is to constantly try and strike this balance. When we are younger and have peak efficiency bodies, we work on improving our minds (going to school, starting careers, etc.); when we are older, we have to work on getting our bodies more in lines with the cumulative efficiency that our minds achieve through age and experience.
No one ever said that this life stuff was going to be easy.