My almost 5-year old son has been into trains for a while now and we recently visited a train store, thinking he would want to get some Brio or Thomas trains. Apparently, he tells us those trains are for babies and he wants REAL trains (pointing at the store’s HO scale diorama). We bought a used Athearn’s HO dummy diesel unit for him a year ago but stored it away and didn’t take it out until yesterday. He absolutely loves it but he wants to see it run on the tracks, I don’t have HO tracks only Z and T scales. He takes good care of his toys, especially his trains. I’m thinking he’s ready to start with a HO set as it’s widely available and something he can expand in the future. I DON’T want a starter set that uses special tracks (i.e. Lionel Ready-to-Play or Marklin My World). Which starter set would you recommend, used or new is ok.