Comment by dmurray
> States make their own age-related rules. The states are part of the US. So technically sure, you're right. In practice, you're very wrong
This is wrong. It's particularly wrong in the way that you draw a distinction between theory and practice. It's so wrong that it's backwards.
In theory, the states set age related rules. In practice, they must set them to what the federal government tells them to. This was established in the specific case in 1984 [0] when Congress realised that it could withhold funding to states based on how quickly they agreed with it, and in the general case in 1861 [1] when the United States initiated a war that would go on to kill 1.6 million people after some states asked it only to exercise the powers derogated to it in its constitution.
[0] https://en.wikipedia.org/wiki/National_Minimum_Drinking_Age_...
Even the age at which you can buy various types of guns varies from state-to-state and that is ostensibly a constitutional right assured to all citizens. In Montana, a child is allowed to buy a gun from anybody other than an FFL. If they're 18 they can also buy rifles from FFLs. They can even buy machine guns if they have the money for it. Meanwhile in California, an 18 year old cannot buy even a single shot .22 rifle, they aren't allowed to purchase any gun until they are 21 years old. Imagine if Texas passed a law saying that you don't get your first ammendment rights until you're 21 years old. This is the America we live in.