Bugs Me So Much How In The US You Can't Drink And Smoke Until 21 But Can Enlist In The Military At 18

Bugs me so much how in the US you can't drink and smoke until 21 but can enlist in the military at 18 (actually as a minor if a parent signs) and you can also enter whatever legal contracts at 18 or take on tens of thousands in debt you can't pay back but you can't rent a car if you need one until you're 21 and you can get a job and have to pay taxes as a minor but you're not allowed to vote on how your taxes are being used until you're 18 but also if you get pregnant at 12 you'll be expected to go through with carrying the fetus and giving birth and might even go to jail for terminating but most drs won't let you make the decision to sterilize yourself until you're at least 30 and/or already have children despite there technically being no regulation preventing you from doing this at 18 and even if you do convince them to let you do it you'll be on a hold for 30-120 days just to make extra sure you're not a dum dum who's going to change their mind and at this point I don't know how we're supposed to define "adult" in this country when we can't seem to come to a single fucking consensus on what that means (read: at what point a person should be granted autonomy over their own body and life decisions).