Mine probably aren't style icons DS 2 is into jeans ,no particular brand, T shirt likes superdry,check shirt again no particular brand , and rugby shirt Wales or Bristol but those are the club's he follows. DS1 t shirts he likes bad rhino but I'm not sure if they do smaller sizes and ice hockey shirts
I'm not sure mine are great examples but ds1 (22) likes jeans from Burton and t-shirts related to gaming or films although will wear primark, Tesco or matalan. Ds2 (20) likes outdoor sports brands i.e. Craghoppers etc. Both of them love the Woolovers jumper I got from the bargain thread.
Depends if he is into clothes or not, if so he will probably have particular (probably expensive) brands he will wear. My 20 yo would not wear the Woolovers jumpers - I got them for his grandad and uncle. He tends to like certain designer brands and also brands such as Patagonia and North Face, high street wise Uniqlo. Uniqlo have their flannel shirts reduced to £14.90. In all honestly i would never suggest anyone buy him clothes unless it was just nice socks.