In a word? YES. Because that's not the 2nd Amendment that would be regulating such. Under the 10th Amendment it would be up to the states to issue age restrictions, just like alcohol. I've fought this ground before, but I maintain that hand grenades and mines aren't covered under the 2nd because they are AREA weapons. Meanwhile, tanks, aircraft carriers and etc are covered under the letters of marque section of the Constitution instead of the second. That section is what gives Blackwater the right to exist.
Do you also think that "libel" and "slander" are unreasonable restrictions on the God Given Right of First Amendment 'Free' Speech?
Before you can apply those charges you have to meet many standards for your case to go to trial and it's very tough to prove them to the satisfaction of most jurists. So slander and libel aren't given as free reign as the right to free speech.
IMO the 10th Amendment was destroyed permanently by Lincoln in 1865.
Grenades and mines are classified under ‘arms’.