Great topic! This is a big one for me right now, as I finally went "back" to school a couple of years ago (at age 35), starting at community college. Before this, I'd worked in restaurants, then retail, then in dental and vision insurance. Now, I'm about to have all my transfer requirements completed, and I've gone back and forth between wanting to be a family therapist, wanting to teach younger kids, wanting to be a pediatrician. I think I've finally found a good way to use a lot of my talents and interests, though, one that won't take six+ more years of school: as a health/sex educator.
I would say you're never too old to follow your career dreams! The only way age played into the decision, for me, was in the fact that I'm nearing the end of my child-bearing years, and have to plan whether I'm going to have a kid and, if so, how that will fit into my schooling and career.
If you aren't sure what your dream career is, I highly recommend a book by Barbara Sher called I Could Do Anything: If I Only Knew What It Was
. I found it mentioned in an article about becoming a doctor, and got it on Amazon for a very low price.