Its not whether you're 17 or 70, its whether you give a shit or not.
I've seen some really good work done by 'youngsters' and some shocking work done by supposed 'old hands' - experience helps, but the care-factor makes the difference.
Tradespeople in the automotive trades are paid poorly. Plumbers, tilers, painters, etc all make vastly more than a mechanic, I guess because house stuff is valued as an investment whereas cars are ultimately disposable.
To be good mechanic requires at least as much skill and uncommon understanding as any good tradesman.
But for as long as we keep paying them crap money, the best and brightest minds aren't going to want to become mechanics.