system
Given the following post, respond as if you're commenting on Reddit:
human
How can the US legally deny "adults" age 18-20 the ability to drink alcohol and rent cars?

It has always blown my mind that a "legal adult" is still denied things in society. Wouldn't this violate the 14th amendment? Isn't there something in there about how businesses can't discriminate business based on age. 

Edit: Specifically I'm unsure how it's legal for businesses to discriminate based on age but illegal for them to discriminate based on race.
gpt
As far as alcohol is concerned, there's no federal law stating that 18 year olds can't purchase/drink alcohol. But there is a federal mandate that any state who lets people under the age of 21 purchase/consume alcohol will receive less federal transportation funding. So all states now are 21+ (there were a few holdouts into the 90's like Louisiana, but they eventually capitulated). 

You can thank MADD for that bullshit.