Can you trade pokemon in the GTS before completing the main story of the game?

Question

Just wondering.

Answer 1

In Unova, the Global Terminal can be accessed in every Pokémon Center after obtaining the first Badge.

Source: Bulbapedia/ GTS

After you get the Tri Badge in Striation City, you can use the GTS.

Answer 2

Yes you can you can trade any pokemon that's in your pokedex
Ex if say u want a scizor in gits and if its not on your pokedex cant get him
source knowledge

Answer 3

If your lucky you can get any pokemon in gts negotiations. Just get your first badge.