I think he meant tanks that were out of service (i.e. retired) by 1939, although what the in-universe rules say about it I have no idea either way.
Near as I can tell, the restriction only applies to tanks that were produced or designed after WWII, so anything else would be fair game. If it were restricted to tanks in service during WWII, then the Maus or the Porsche Tiger I would hardly qualify.
Huh? You want an A7V!?Even if we are to get 12 more comrades, it'll be okay!Then I'd like a Tiger.Is anything fine?Well, that'll be a problem.I don't want it if it won't be us 6 all together.Why?Here's the request formsBecause 18 people can ride in it!!But, if we get a Tiger or a T-34, those only hold 5 people. 1 person gets left out.YES!!The Student Council's got funds to buy a new tank. If we have any requests, we're to write them down.A strong one! Let's get a strong one!Speaking of that, after the final battle, there were a lots of girls in our class who've became interested in Sensha-dou. If there is an opportunity, they would like to give it a try, they said.