My son also loves trombone v much. He has been on it for half a yr already! He also started at the age of 6. He chose it himself and he thinks it looks great on playing trombone cos it's like 發射大炮when playing it...... So I think boys may prefer trombone cos' it looks so powerful
P.S my boy's hand also not enough for the sixth position, so a bit out of tone when he plays the "C". But it's ok as long as he enjoys it and is willing to practise it.