When can you go on the ss aqua?

you have to beat the elite 4 and champion lance then credits come on watch them then the game will reload and you will be at home go downstairs mom says prof. elm wants to talk to you go to his lab and he will give you the s.s. aqua ticket fly to olivine city go to boat place and prof. oak will be there he will talk to you then show your ticket to the sailor and he will let you pass then talk to the sailor in front of the entrance to the boat then you are on the s.s. aqua

hope this helped