I worked in my dad's construction business from about age 10 through age 21. Started doing the dirty jobs, stuff you wouldn't dream of sending a kid to do nowadays, like going up into a hot attic to lay down fiberglass insulation. My dad gave me a pair of his old army fatigues, goggles, and a cotton face mask, which I suppose was better protective gear than typical for the time. I still feel itchy when I think of doing those jobs.
At some point I graduated to trim work and finish work, and one of my favorite jobs was installing trim, doors, fixtures, and hardware in a finished home (I was a whiz at hinges and door knobs around age 12, and thought it was fun). Eventually I learned every aspect of building a home and commercial construction, and years later it would serve me well. I took a mostly hands-off approach when my wife and I used a general contractor to build two homes decades later, but being able to double-check stuff, take on certain jobs, correct minor issues, and know how to talk/interact with the subcontractors as equals was great. I made great friends with those guys instead of the typical "customer" interactions you see all the time when building a home.
In retrospect, one interesting thing is that I learned how to *do* all that stuff back then when I was a kid, but didn't necessarily *understand* why we did it that way or think about if there was a different or better way. As I age and tackle many new building projects on our property, now I spend more time understanding things and it really is illuminating. For instance, when I cut roof rafters now, I think about the bearing area of the birds mouth on the header, how the rafter attaches to the ridge, how different species of lumber affect load and deflection, how to properly attach rafters to handle wind loads (no more toe-nailing like the old days), etc..., and there is a lot more to it than I ever grasped as a kid.
The other important job was from age 17-21, while I was at college. My work study job was in the engineering school machine shop. Started out cleaning off the machines at night, mopping the floor, and general maintenance. By junior year I was fabricating stuff and the head machinist took me under his wing and trained me. At one point he told me I should be a machinist instead of an engineer, which I thought was silly at the time, but realize now it was high praise from a machinist. I loved that job, especially the feeling that I could make anything out of metal and fix anything. For years after I left college, I lamented that I no longer had ready access to a lathe and Bridgeport, and felt crippled without them. Occasionally I would get a chance to get on a machine and was in heaven. I don't really have a need for those machines anymore, but one of my goals when I retire is to have a lathe and Bridgeport so I can tinker.