Is this due to genetics? I’m unsure…

23M with a 8.5-11.3in. fully erect, rock hard. Of course, my dad is huge too(8.15in) (fully hard), but compared to him I’m noticeably bigger, i checked multiple times (I reached this length around age 12-13). I don’t know why that is—maybe the large size comes not only from genetics but also from differences in our growth environment?