He has wrinkles! And grey hair! It’s quite appalling; he hasn’t looked this old since his first regeneration. Even at the end of his previous regeneration, after living such a long, long time in the same body, he hadn’t looked this old. Had he? It was hard to remember, he’d mostly only seen his reflection in Handles’ shiny surface and it was always a bit distorted.
But he doesn’t want to look old, because he’s not old, not for a Time Lord. That’s the trouble with regeneration; it never takes his preferences into account, just gives him any old body!