Being a plumber can be brutally hard work (think cast iron bathtub/stairs) and isn’t a job for the 50+ age set. You also don’t make great money unless you’re the owner. Still, I would encourage my kids to do that if I knew they would manage their money well enough to retire early.
HVAC – another high-paying job for the owner, but imagine replacing an attic furnace in an inland empire summer.
Anecdotal – I know an early 40’s crab fisherman. He works two seasons per year (6-7 months total?) and makes over $150k in that time. He’s got seniority, so he doesn’t do the dangerous work anymore – he sits in a nice warm cabin operating the crane. I’m not sure I would ever have been willing to put in the work he did to get to that point, and probably physically incapable now. He says that most 20-somethings wash out after one season.