Amen!
Never, never, never, never....NEVER take anything the BATFE provides you verbally as fact. Far too often they don't know the law themselves and if you quote the USC and State laws verbatim you'll just tick them off. They DO NOT approve of an armed citizenry as it prevents them from running completely amuck.
That said, even though it's not illegal to make a private sale of the nature we've been discussing you all had better realize very quickly that it only takes them penciling in a rule change to make it illegal. They'll call it a clarification of sorts. So it's really not worth the risk if that person cannot buy on a Form 4473 you should not sell to that person.
The law needs to change to where an 18 year old that can be called into military service, can willfully serve and die for his or her country, and can vote should not be restricted from lawfully purchasing a firearm. I've witnessed plenty of 21+ year olds that don't have enough common sense to walk out their front doors on a daily basis let alone anything else. There's no way the Fed will ever be able to prove cause for "maturity" between 18 and 21, it's just not there across the board.