I walked away from my trade around forty, and I'll be honest with you if you truly want to do a certain trade, just do it. I've said it before, and I mean it: some trades can be brutally hard on your body over the years, and that's something you really have to face with open eyes. Don't fool yourself into thinking a bigger paycheck after the trade automatcally means a better life. On the brighter side, a change can feel just as good as a holiday, and you'll never feel more motivated at least for a while. Just be careful when you pick your trade, so that motivation doesn't fade on you.
PS if you love working on cars, don't become a mechanic.