@lisa It's definitely not too late! But having some structure is important, especially for beginners.
I haven't used Duolingo myself, so I'm not certain, but I suspect some of the key problems with it are a degree of incoherence in content (e.g., it's not part of a coherent curriculum) and insufficient opportunities for the learner to actually use the language in meaningful interactions with others.
Is he certain he can't enroll in a class? Perhaps pass/fail? Or maybe a summer intensive program? If not, another option might be to try to find a tutor. But if he does that, I recommend working through a textbook. Not because there's some perfect textbook (there isn't) but because it's a good way to ensure you're not missing important learning tasks.
I will try to come back this weekend and write more, but I will say that I am a "success" story, in that I didn't start studying Japanese until I was 24. I started in a summer intensive program (where you do a year's worth of college-level Japanese credits in 10 weeks), then did an academic year of college Japanese classes, then another intensive summer program (10 weeks), and one more academic year of Japanese classes. Then (after completing four years worth of major credits in two calendar years) I graduated and went immediately to Japan.
In my case, I think something about those intensive programs was important, and the second summer especially mimicked in-country immersion (because we had to live in the dormitory, our teachers lived with us in the dorm, and we were only allowed to use Japanese 24 hours a day for the whole summer).
Anyway, I'll come back on the weekend and try to give some more actual advice. but it's definitely never too late!
