The North Face Men's S/S Simple Dome T-Shirt

My son is an aversge size 14 year old what size should i buy him

is this t-shirt real?

Hi my partner normal a size large but put little weight on so if order a soze xl will it be easy to chance of dont fit ??but will be after xmas that o

true size? If an XXL will fit a chest circumference of 135cm, then a direct measure of the width of the shirt (under the arm) should be around 70 cm?