Noted. Your position is that it is ok for the goverment, just not the Feds, to deny certain activities, which cause no harm to others, to its citizens soley based on an arbitrary age limit.
No. That is not what I said. I quite clearly stated that the Age of Majority, where you could make those decisions for yourself, can be set at the State level. It is still up to the parents/legal guardian to ascertain which behaviors to allow/disallow. Any actual crimes committed by said children are also the responsibility of said parent/guardian.