As I sit here in Aldie, Virginia . . . if I was a high school student around here and had to do it all over again, then I would become a plumber. I'd either go to tech school for it or just work for a plumbing company to learn the job for a few years, and then I'd start my own business. I assure you that I'd be rolling in big money within 5-10 years. So many people around here make lots of money, and very few of them have the ability and/or the time to make even small repairs. The same is true for HVAC. No college degree is required in either of those fields.
The issue/concern isn't the first 20 years of those careers, it's the last 20 years.
Both of those are physically demanding and you don't see a lot of old plumbers or hvac techs, in part, because of the tax it takes on one's body.
SSDI and work comp claims for physically demanding trades are significantly higher than claims from office jobs. That should be obvious, but it sure seems to be ignored when everyone gushes over how you can pull in 60k at 20 years old without a degree.
And for everyone that says 'once I am older I will just run my own business'...well you know what helps do that competently?...a degree in any number of business related fields.
There is a reason whyhome maintenence based trades are often either a large established company or a single owner/worker. The small business fleet style is brutally tough to manage.