I had similar feelings a few years ago and made some drastic changes in my life. I was in car sales and was fairly successful, made good money and really loved the peope I worked with. One day I just had enough and went to the local community college, signed up for classes and quit my job. I pulled all my money out of my 401k and went to Cali with a girl I adored for a couple of weeks and then started classes when I got home. I have an associates degree and I'm a year away from my BA. I will be a teacher by the fall of '07. I love the thought of teahing and I think it's a great way to give back to society. The downside is I will be making less money than I did before with an additional $40,000 in debt due to loans, I am broke and was forced to move back to my parents house. I think in the long run it'll be worth it.
I guess the only advice I can give is to follow your heart and it's never too late to make a chang in your life.