At 18 most young adult’s brains are still developing and maturing. Along with being taught how to use a weapon of war by the military, one is taught discipline, proper usage of the weapon, and weapon safety as well as personal responsibility and group responsibility. I have no problem with an 18 year old member of the armed forces have the right to carry.
But many 18 year olds with out this supervision and training have no business carrying a firearm. Most lack the maturity to understand what they are doing.
An example is the kid 18yo Senior at FRA in Nashville who, while riding with his GF, brandished a pistol at a young lady who brake-checked them for tailgating. He was kicked out of the school and faces felony charges.