Any law that restricts an act based solely on age should coincide with the legal age of majority, which is 18 in the US. it's the age when a person can do these things without parental or guardian permission:
- enter into a binding contractual agreement
- enter the military
- marry
- vote in federal, state and local elections
- register for Selective Service
- change your legal birth name
- serve on a jury
- file a lawsuit
- create a last will and testament
- open a brokerage account & buy stock in your own name
- open a bank account on your own
- apply for credit cards
- buy real estate
- apply for a mortgage
- rent an apartment
- engage in pawn shop transactions
- get a Big Box membership of your own (Costco, Sam's Club, ...)
- file for bankruptcy
- control your own medical decisions
- give consent for vaccinations
- donate blood (may be 17 depending on state)
- designate yourself as an organ donor (may be 17 depending on state)
- obtain medical care at an ER (may be exceptions)
- purchase cough suppressants and other OTC meds
- use a meat slicer at your place of employment
- become a realtor
- become a notary public
- work in a bar/serve alcohol
- drive a cab
- get a commercial truck license
- work a full time job while attending school
- get body modifications
- travel without parents' consent (public transportation)
- purchase a lottery ticket
- buy alcohol outside of the US
- purchase a pet
- access adult XXX stores and content (yeah, I know ..)
- skydive
- book a room at a hotel
- buy fireworks
- bet on a horse race
- be free of curfew restrictions (some exceptions)
- buy spray paint
- be home alone to admit a service repairman into the home
- buy a car
- apply to locate biological parents
- adopt a child
- move out of parent's home without their permission
- obtain a driver's license without need to complete a driver's education course (most states)
- be arrested, tried and convicted as an adult
I'm sure there are more, but the point is, the age of majority is what ought to matter. Any other age used to restrict a person's rights is inconsistent, capricious and arbitrary.
https://en.wikipedia.org/wiki/Age_of_majority