My son is 9 as well and he's been playing pinball since about 7 years old. He has quickly become a very good pinball player and came in 7th in a 35 person tournament last summer. He's currently doing great in a local league. His absolute favorite machine right now is Attack from Mars with Addams family a close second. We have three machines at home Munsters, Stranger Things, and F-14. His order is probably Stranger Things - Munsters - F-14 (doesn't really play that one). As he gets older I'll probably get deeper machines but for now these are good.