He has quite some looks of a Norwegian Forest Cat. As he is big, and matures late, I would guess he does has much of NFC or possibly Maine Coon in him. NFC has also quite often such a color pattern.
But if pure bred, not of Show quality.
By he has not matured yet, you mean, he is not neuter yet? If you arent a breeder, the best is to neuter. Even if some toms manage to be essentially spray free, and without big problems the whole life.