Yes! He is very, very skinny!! With the thoroughbred in him, he'll probably need pretty big increases in feed to make it through the winters without getting all ribby like that.
When winter first hit here, my TB/Paint cross started dropping weight fast! Partly because I stopped working him daily, and also he just needed more food since he was burning more calories to keep himself warm (and the lack of grass in his pasture)! I upped my horse's hay by 400% and his grain by 800%. I also added sweet feed which gave him some sugar boost.
With your boy being in his late teens and in such cold climate, I'd really give him more to munch on!
He does have a cute look to him and seems very alert. It also looks like he enjoys your company as he seems to lean in to you as you're taking the photos!