We already have this system of "wait until you're older for..." with alcohol. Renting a car. Turning 18 grants the right to vote and consent to sex. Live another 3 years and you're considered capable to handle alcohol, sometimes this assumption is wrong. At 65 the american society has deemed that you have the right to retire and collect social security. Why not have another milestone at age 42 that says you can now legally carry a concealed weapon in consideration that you might have acquired an enemy in 42 years of life and you feel the need to protect yourself. The proponent is that one side satisfies a human desire and it is marked by age. The other lumps the whole spectrum of rights into a certain year. The difference seems to be that one is more thought out.