The Elite 4 is an option to train all of your Pokemon, since they are at very High LVs that range from the 70's. You can battle your Rival Cheren everyday in the Victory Road after you see him in Route 5. If it is Spring in your game, you can challenge the Sinnoh champion Cynthia everyday in Undella Town. The last Trainer you can battle everyday Is Game Freak Morimoto located in the Game Freak building in Castelia City. I Hope this helps.