I have a very skinny average height 15 year old who has one pair of H+M super skinny jeans from last year. He loves them and they fit well but are knackered now! I ordered a replacement in the 14+ and they are totally different. They are Extreme Flex I think but are massive around the leg. I looked in the adult ones and they are big too.
Where do your skinny hipped/legged teen boys buy their jeans?!