How about the same number that lets you vote, and decide where you live, or get drafted, and get married without parental consent, and get medical care without parental consent?
Voting, moving out, getting medical care, and marriage generally don't negatively impact your body and brain.
Alcohol, weed, cigarettes, etc. all do some kind of damage to your body. If anything we should raise cigarettes to 21. And yes, even weed, especially smoking weed, does damage to your body, even if it's massively less than the other two I said.
(And getting drafted... well that should just go away all together).
For sugar, what do you actually ban? Added sugar? There's plenty of sugar in fruits, especially when you juice them. How do you enforce this? Seems like a nightmare to figure out.
Caffeine is interesting. It's actually physically addictive. I can't find any studies on long term effects of caffeine in children, though.
And, of course, there's exactly 0 support to do any of that, which can't be ignored. Probably a better use of everyone's time to improve health education.
Regulate medical marijuana like any other non-scheduled drug and leave cultural decisions concerning recreational use to the states, where it belongs. Use federal funding stipulations as leverage when needed.
I didn't mean to imply that it was any less arbitrary (the arbitrariness of the numbers is disputed in other threads), only that I view the feds setting that number as overstepping.
Weed is still somewhat dangerous to smoke because of lung cancer and we regulate cigarettes so there's some precedent here.
On the other hand, there are methods with which to use weed that confer 0% risk of lung cancer and my anecdotal evidence suggests more and more people are using those methods.
Vaporizing, or using edibles, or other concentrates, eliminates that as you aren't burning/combusting anything, which is where most of those harms come from. There are plenty of ways to ingest now without actually smoking it. You can even get chocolates and gummy bears in legal places.
At the weed shop I've gone to a couple times, the people there said over half their customers are buying edibles. Most people don't want to inhale smoke, not just because of the health concerns, but because of the lingering smell.
I smoked it once, and I hated the taste. It left a lingering taste in the back of my throat.
All I ask and hope for is consistency in the law. We shouldn't use reasons like "it's a forming brain" to shoot it down in one drug context while ignoring it in another, totally legal drug context. Alcohol is a drug, period. A very destructive drug, and it's completely legal for anyone of age. If cannabis is too destructive to young minds to be legalized, so is alcohol and we have way more scientific evidence in that case. Let's just be consistent.
21?
Haven't we as a society progressed past this pernicious discrimination!