The mass use of fake IDs of this sort is a bizarrely American problem. In the UK, you're considered an adult at age 18. Most (aside from the unfortunate 17-year-olds) university students can legally purchase alcohol, smoke, or gamble if they so choose. But we don't have MADD, I guess.
Also, under 18s probably still want to be served. I was 14 when I first tried to get served in a bar (barman sold a 16yo the drinks, then came and confiscated them; canny barman).