There have been various debates for quite some time as to how old a person should be before they can buy firearms. Generally, folks over 18 & under 21 can purchase long guns and ammo, but for handguns and handgun ammo an individual needs to be 21.
I see a conflict here. I entered the US Army at age 17 (with parental consent) and was taught how to use an M-14, a 1911A1 45 and various other items. At 19 I was in Vietnam and became familiar with the M16 and the M60. Now, in today’s military we have many individuals who are under 21 and are highly trained on various firearms. In places like Irag, Afghanistan (and yes Vietnam) it is not only the combat soldier that has to know what to do, non-combat personnel are thrust into situations that require action. Our military personnel are not only taught how to use a weapon effectively, they are also taught other important skills. These include proper maintenance and cleaning, and very importantly, safety.
Add to those who have or are currently serving are many people who are under 21, over 18, and who have obtained laudatory skills with firearms. These are individuals who have gone hunting with family members, participated in organized shooting competitions, and may also possibly belong to a JROTC unit. They have taken various safety classes including many sponsored by the NRA. They understand what a firearm is, what it can do, and how to safely use and store one.
Arbitrary age barriers are nonsense. Training, education and skills are, IMHO more important.