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.
Your bizarreness may be misplaced. American 18-year-olds can smoke and gamble. I don't see how 18 prevents fake ids from 16 and 17 year olds though.
And 21 is the gambling age in many states in the US.