my boyfriend has a small penis

Love.peace.happiness
My boyfriend and I are 1 year apart he's 15 turning 16 and I just recently turned 17. He's 6'1 but When he's hard he's about 5 inches when he's soft he's like 3 inches, will it grow?? Is he done growing?? I mean I'm fine with his size now but I'm just curious ? When will puberty hit? Will he be this size forever ?? Or like what?