The two youngest teenagers are 14, and the brothers of RedNut (one from Dad's 2nd relationship, one from Mum's). There is NO way in heck he will allow them to drink anything, as he is trying to ensure they grow up to be responsible young men. The others are either 18 (I still call call them teenagers - ends in teen, you're a teenager) or their parents don't care. Our home town is really bad for underage drinking, drug use and vandalism, and since the introduction of a $4000 baby bonus, teenage pregnancy. Lots of parents are of the mind "How can I stop them, they'll just do it anyway?".
Thank you to everyone who has posted on this thread. It has put my mind at ease that I wasn't being a screaming loony about charging guests.