Tbh lots of 14 year olds take weed and drink... I've been drinking since i was about 11 ... not done me any harm( i think
)... I had weed at 14... Most people will try it at least, and if your brother wants it, twatin the 18 year old wont stop him gettin it in the future. From here it sounds it was your brothers fault as much as the 18 year olds.
Plus drinking and weed is pretty much harmless
Edit: Reading that it sounds abit bad, dont get me wrong im not saying the 18 year old is an angel, but, it happens alot these days. I know quite a few kids near me who been drinkin/smoking since they were younger than your brother.. All it does is make em abit chavi-fied and gets them hanging around with the wrong people.
If the 18 year old stops givin him drink, he'll get it somewhere else... if he wants weed and 18 year old wont give it him.. he'll get it somewhere else. End of the day, you'd have to go on a rampage n kick shit out of all the local dealers in your area.. and he prob still be able to get it. Plus kicking off with dealers aint a good idea... They are normally little geeks but they have friends.