Kinda hard to tell from the photos, but he doesn’t look all that thin to me. Carpets are very long, slender pythons. I’d give him a bit to settle in and then offer a small rat just to gauge his appetite. He could surely take a medium if you feel inclined to go to the pet store for a bigger feeder, but at 10yrs old he’s done most of the growing he’s going to do and shouldn’t need an overly high calorie diet to maintain his physique. Welcome home, Squeeze/Hugs!
As a carpet python owner I'm going with this - at 10 years old he's done growing. A small rat every 10-14 days so he maintains his weight should be fine. That's all my male gets and he's bigger.