Objectively speaking, he's probably improving in all kinds of ways. Going downhill from where he had been immediately after Starkiller Base would have been next to impossible. The environment has been helpful, too; he had to struggle to keep the light side at bay when he was surrounded by the dark side, and now he has little but light around him.

Still, Kitty probably sees more improvement than there actually is.

"I would have guessed older."