One of my cousins was similar. He was always very smart but just not into academics. I think he was mostly into working on his old muscle car and smoking weed, to be honest. He stumble-bumbled around for a decade after high school, working complete shit jobs, including his final 4 or 5 years working at the city landfill in Fort Worth. Then finally one day when he was about 30, he decided he didn't want to be a burnout for the rest of his life, and he got himself into Texas A&M where he went straight through in 4 years and earned a software engineering degree. Ever since, he's worked his way up from coding, into senior management, at a private software company in Dallas. He made great money, got married, and actually just retired a couple of years ago, before age 60.
That got longwinded but I really love late bloomer stories like that. They tend to make me happier than success stories about people you always expected to succeed regardless. Anyway, best of luck to your stepson.