My son was 11 when we cruised, and he did not own a jacket. I didn't feel it was worth the expense to buy one when he would not be wearing it again and would likely outgrown it even sooner...on formal nights he wore dress pants, a dress shirt and a tie and he looked very handsome. He fit in well with everyone else and we got some great pix. If you already had a jacket, I would certainly bring it, but I didn't think it was worth buying one for the cruise.