I have an X220 with an i5-2520M, I don’t use it for gaming but I have briefly played Half-Life 2 with it and it was comfortably playable.
So I would say mid-2000s titles and before will be fine. It really depends on the age the Thinkpad you want is, and the age of the games you want to play.
They are fairly crap as a hand dryer too.