Well,you can join the Army and be trained to kill people you,ve never even met and in extreme cases be drafted against your will for the same thing when you,re 18. Seems to me there,s something screwed up about that too.If you,re not mature enough to drink alcohol,you,re not mature enough to survive combat without serious mental problems. That said I,d go for the 21 years to buy a gun if the age to join the Military is raised to 21. However,it,d probably be harder to get a bunch of 21 year olds to charge a hill than a bunch of 18 year olds.More mature,less amenable to bullshit. I,m a Marine Corps veteran,been there,joined at 19.