The liver is a strange organ. I knew a Alcohol Addiction Recovery specialist.....or whatever you want to call it.... explain it to me.
When you first start drinking it it is easy to get drunk fast. Then after a while you begin to build up a tolerance to where you can drink 12 to 20 or so beers and handle it pretty good.
The problem is if you continue to do this for a couple decades you pass your "peak" and the liver deteriorates and is not able to process the alcohol as well.... This is why you will see 30 year nonstop constant hardcore alcoholics who can only drink a 6 pack and get shit faced...they have already fucked their liver up to a point that it doesn't work properly, and they are no different then the 14 year old who is drinking their first bottle of Boones Farm.