I don't think I've ever seen it asked before and you're not going to get an official answer here, Beta maybe but not here. My assumption is the only things that move a special building from one age to higher ages are Reno Kits and 1up kits, an exception being wishing well of course which does so all by itself. I don't think specific building upgrades are age specific, rather the building itself is which is determined by the age you won it in, so if you won ToI in Iron Age and won upgrades for it while you were in EMA or use upgrades for it you won for it from an earlier age while in higher ages the building would still be IA after you use the upgrades.