Alcohol is bad for tongue piercings. Listerine and other alcohol-based mouthwashes are not recommended for use after a tongue piercing, so I presume the same goes for beer and such. You can still drink it, it will just irritate it and take longer to heal.
After the first coupla days, he'll be fine. If he really wants to drink before then, I suggest margaritas and other frozen beverages. They were fine for me and mine healed superbly. Beer after 5 days I wouldn't worry about. Worry more about dairy-based foods and spicy stuph. No Indian food.
You don't want that sh!t in your blood stream. All you need is the alcohol in your blood to get drunk. So go get some Everclear, or something similar, & distill it to get pure alcohol. Or, if you can find some 200 proof, use that. Otherwise you're just ASKING to end up in the hospital. Of course injecting pure alcohol into your veins is also a good way to end up in the hospital...
That's because you're a "good little boy." That's probably true for more of you than I would care to know about, but hey... I don't want to find out in the first place.
Anyway, yeah, everclear would probably be better anyway... You know... if you wrig it right, you can completely remove the blood and replace it with the stuff. That ought to give you a little bit better buz than you're used to, I think.
Napalm... Listerine is the recommended mouthwash after getting your tongue pierced. Every tattoo parlor i've been in sells listerine or gives out a sample for you to use.
If you keep your mouth clean and wash it out every hour or so while you are drinking, you should be fine, but you might want to wait more than 5 days, more like a week and a half to two weeks. (Nasty mix---beer and listerine..ewww)