Anybody successfully pull off a career change? How did it go?

Curious because I'm looking for work. I've been an unhappy accountant, teacher, most recently underpaid law office paralegal, and now my friend is trying to convince me to become a truck driver because it fits my personality. I've know a few people (mostly military) who have made the transition well, but I feel like it's only young people who pull it off these days. I'm 30 and don't know if I'm young or old.