Learning to be a top-flight mechanic could be a spring-board to bigger and better things. And if you dedided to go to mech. engineering school in your late 20s, you'd have a great job to fall back on to pay for school.
Also, studies have shown that people who have done hands on techincal work have a leg up in engineering studies. It's like your hands learn stuff that your brain stores up.
I wasted a lot of time in my youth -- the old saying, "The wages of a mis-spent youth" haunt me a bit. I still can't weld, and that would be a nice skill to have under one's belt. I can solder like nobody's business though.