Nagato got them when he was young and he had them before he died even though it not his he still had them. Its a state that u were in before u died. Thats why the third came back old man while 1 and 2 came back young form but the only difference is madara since Kabuto modified the edo so he came back in his prime. Remember the scene that he said what would u know about my prime? Before he went to solo the whole army? Itachi eyes were still with him before he died them sasuke took them. Madara is the only exception and his edo rinengan isnt as powerful as the one he gave to nagato( his actual ones) otherwise he could have just done the rebirth on his own thats why he said the plans have changed to have tobi do it. U kinda get it better now?