My wife recently bought me a pistol as a gift. When the gun shop owner found out it wasn't for her, I had to come down to the shop and fill out the forms for the transfer myself. But this is California.
Maybe your Dad should "loan" the gun to you after he buys it for himself, and "give" it to you when you turn 21, transferring it if he has to at that time. Until then, be very careful to obey all laws while transporting your Dad's gun to and from the range. Have fun and be safe.