§134-4 Transfer, possession of firearms.
(a) No transfer of any rifle having a barrel length of sixteen inches or over or any shotgun having a barrel length of eighteen inches or over, whether usable or unusable, serviceable or unserviceable, modern or antique, registered under prior law or by a prior owner, or unregistered shall be made to any person under the age of eighteen years, except as provided by section 134-5.
This is what made me think 18 was good for long guns and 21 for pistols. Why would they include this?