I'm a personal fan of the Pour House and McGreevy's. They are both on Boylston St. and are right next to each other. They serve food there, so if you get in early enough they aren't checking IDs at the door and your friend would be fine. If you are wanting to not go until like 11 or something there then may be an issue. There are a lot of fun places around though, so other suggestions might work more.