From Ammoland:

Where the gun issue comes into all this should be obvious. Look at all that’s being done to limit access to rifles and handguns to anyone under 21. If you’re a “minority,”  Mike Bloomberg wants it to be 25.
As a matter of historical perspective, Audie Murphy would have been deemed “too young” to be trusted with a rifle at the time his legendary heroics earned him recognition as the most decorated combat soldier of WWII. It also flies in the face of 10 U.S. Code § 246 – Militia: composition and classes:
“(a) The militia of the United States consists of all able-bodied males at least 17 years of age…”