I don't think my dad and I ever built anything together before I was 19.
Of course, when I was 19 and we tried it* we found that we were both perfectionists committed to doing the job right, we didn't always agree on the details, and we were both willing to firmly stand our ground about what we believed. The -- ehem -- "engineering discussions" tended to raise the roof.
* Building the mock-up for the 1939 Ford Convertable body that Wescott's Auto Restyling builds -- we basically made temporary molds of every panel, then built a body by hand from the individual panels ala Corvette. Much measuring, cross-measuring, leveling, hesitating before gluing things down, arguments discussions about whether everything was square and straight before the glue was mixed, etc.
The mold came out nice, though.