I just turned 18 and bought my first ar about a month ago and love it. Wanted to get an Ar platform pistol but you have to be 21 to my knowledge. Can I buy a stripped lower and buy the trigger control group, buffer tube, ex. and a pistol brace to make it a pistol then get an upper with the barrel length that I want? A post I previously read said that a stripped lower that had never been a rifle can be made into a pistol no problem because it was considered just a receiver.