Also absurd and unconstitutional. You can make a rudimentary gun out of plumbing parts from a hardware store that is at least as effective as a 3d printer, arguably more so if you're looking at 100% printed parts. Should we run background checks at the register at Home Depot? Should you not be able to buy plumbing if you made some bad decisions and served the time?
These are all ridiculous laws designed to restrict the liberties of the common man.
There's no way to enforce an age ban on anything Internet related without serious privacy violations.