Growing up, I didn't know what was possible. I was the first in my family to even graduate High School (seriously). It took a bit of luck of circumstance, and a lot of hard work, but I've learned something special.
I firmly believe anyone can move into another career if they just decide to do it. I believe I could pick a career, and work hard to achieve it, and succeed. Pretty much any career I wanted. I know, because I've done it twice, and I know I could do it again.
I had dropped out of college and was working as a restaurant server when I was 23. I decided, sort of on a whim, that I wanted to go back to school and be an engineer (for the money). So, I got accepted into a University, moved near by, and finished my engineering degree in 3.5 years. I was working for $55k/yr at age 26.
After a couple of years, I was 28 and decided I wanted to be a teacher. It would be less money, and I had no experience, but I made it happen. I was teaching a year later, and loving it, even though I only made $40k.
I've since gone back into engineering, for the money (made $70k last year), but that's not the point. You can do anything you want. Just DO IT!
If you say you wish you'd have gone to school to become a Dentist, but now you say "That ship has sailed". I ask why, and you say, "It'd be 5 yrs of more school! I'll be 5 years older!" I say, "How old will you be in 5 years if you don't go to Dental school?"