Why has my tolerance gone up so drastically?

I was a very light drinker between the ages of 17-22. Now I’m 28 and can gulp down a 0.5-litre bottle of Olmeca Tequilla and perform regular chores without any difficulty. Mind you, I moved to a new snowy country 8 months ago and have only consumed alcohol 4 times so far. My BMI isn’t too disproportional either. What’s changed? Is it the fact that I grew obese from drinking too much between the ages of 24-26? Or is it something else?