Ok I am currently playing through the ruby game. Would it be possible for me to effectively ev train after my pokemon is like level 70? Because while I'm playing through I don't want to ev train until I am ready.
Many people actually prefer to finish the game with an untrained team, then breed new pokemon for nature and/or IVs and EV train those pokemon as their competitive team
This. Just get your starter and one additional pokemon (to battle the starter's weakness) to a decent level. You can use the item Exp Share on the second pokemon for easy leveling. Keep all your HMs except Surf on the last 4 pokes in your party (Tip: Wailmer and Tropius can learn them all as a pair, leaving room for a Pick Up poke and a Paralyze poke for catching). Make sure your starter knows a diverse set of moves to be able to one-shot as many types as possible, and your secondary poke fill in the gaps. A 55ish starter and 40-45ish secondary pokemon can tear up the Elite 4 with some clever potion use (Switch in a useless pokemon when you need to potion).
Once the E4 is down, you have all you need to efficiently train your dream team. You can access all areas to catch what you need, you can fly around quickly, and if in Emerald you can clone. Perhaps most importantly, you have a perfect exp site in the Elite 4. Just put Exp Share on your poke-in-training and tear up the E4 with your old starter. Make sure you spend all the money on pots/vitamins etc before going in so you can die safely when/if you run low on PP.
Once you have a new EV-trained poke at E4-killing levels, you can rebreed your starter (if female) or EV reset with berries (if on Emerald). Or just abandon it in favor of some new specialized EV trained monster.
EV training before the E4 is unnecessary, boring, and takes far longer than just doing it after the E4. The only exception would be if you wanted to use your Legendary catch on the E4 in non-Emerald. You should consider EV training that one since it can't breed.