Do it, don't hesitate.
About 2 yrs ago I asked CP if I should do this, and the overwhelming response was yes.
I was 36 and bored to tears of my career, and now over 2 yrs later I'm working in a field I absolutely love and couldn't have been happier with my decision.
I found that the age didn't matter going back, you'll be shocked at how many people are doing just what your thinking of doing, plus of course the added bonus of the females are still young and lovely
With grades I also found things way easier than when I was in my 20's, its because now I'm doing it solely for myself, not for my parents or anyone else. Studying became almost fun, still hard work but at least you approach it all differently, this is your money your spending and you take things way more seriously without forgetting to enjoy it too.
Jump into it, get excited and don't look back, the worst case scenario is you blew a few years learning new things, meeting new friends and enriching your life. If anyone wants to tell you to not waste time and money on this, they are either stupid, or well stupid.