What if someone from the office invites me for drinks but I'm underage?

What if someone from the office invites me for drinks but I'm underage?

That's fine to say, "Hey, I'm not twenty-one". Does that mean that you can't go out with them? No, what that means is that you should just order a coke or don't order an alcoholic beverage. If you order a coke or a water or something and you think, "Oh, I'm such a loser", then yes, you are a loser. But if you go with the flow and say, "Oh, I'm under twenty-one, I'll just have a coke", just be outgoing and it'll be fine. You don't need to have beer with them.