First off, he's not saying he's intellectually mature. He's saying he's almost a full-grown adult, which he is in both a legal and physiological sense. Second, there is absolutely no correlation between homework progression and maturity. I do my homework in the early hours of the morning on a consistent basis, and you're in no position to judge me for doing so.
ik you're all about this "I'm strong so I can do whatever I want" thing and all, but that's actually meaningless if you can't get and keep a job
so school is important, and bc of
that, grades are important, and homework is important for getting good grades. so ya, you're right, homework has no direct relation to responsibility but if you don't recognize the importance of it and do it when you need to, that is a sign that you lack responsibility