18m I have to drink a lot to get drunk

I live in Australia legal drinking age is 18

I have barely drinked in my 18 years on this earth but for some reason when I do I have to chuck down a crazy amount of alcohol before I’m drunk. I am on the heavier side 6ft 1 113kg / 250lbs I think. But my mate 5 ft 11 is 103kg and he gets drunk off like 6 beers and so do all my mates while I’m off 15 shots and 3 8% drinks and then I finally feel drunk and I stop cause I don’t like being to drunk and we’ve tested it with a mates expensive breathalyser after 9 pints of Kilkenny my mates were over the limit while I was still far below I was born at 26 week’s gestation so my first thought was oh my liver is fucked but went to the doctor they ran a bunch of tests and my liver is healthy. can it be genetic cause me and my cousin can drink a lot he matches me but pukes later that night and it’s not like I’m already drunk me and my mates have done mini games like reaction time, memory , balance, space awareness ( close your eyes navigate through the rooms and try to find a designated point aka the bathroom. And I outperform them every time even with more drinks. It’s really good for a long party but when it’s just me and my mates. And I need most of a carton to myself it’s just not cost effective. I’m wondering if there’s is a explanation I’ve got Irish and Scottish blood in me I heard they can drink but don’t know if it’s a myth the only person that can slightly match me is my cousin which had Scottish and Irish blood in him. Is it genetic cause it’s really annoying spending half the party getting drunk instead of spending most of the party drunk.