I'm a high-functioning alcoholic and have been drinking since I'm 12
Have you ever stopped drinking?
I stopped for some time but after some years I fell back into it
Excessive drinking can increase your risk of serious health problems, especially when you start at such a young age. Even just cutting back on the amount of alcohol you drink is usually a very healthy thing to do.
I've always been fine with it. It's not like my liver could explode.
It's true that the health effects of alcohol will not come on suddenly, but they will build up over time, and you could face severe illness in old age.  Furthermore, when you drink today, you face serious risk of car crashes that could kill you or others.  Neither of these things are worth the short-term joy of drinking, so you should really cut back, and try to quit entirely.