You can only trade to other games as long as it is in the same generation. Why? Well the the Pokemon may be or have:
But You can Migrate Pokemon into a newer gen, you can't bring it back though.
From gen 5 to 6? no.
The only way to transfer Pokemon from gen 5 to 6 is via Pokebank.
If you are talking about gen 4 to 5, also no because the GTS doesnt work anymore.
Source-experience and logic.
I believe so,as long as You putit in before the Internet option was terminated on previous gens.!
No. The internet services for the previous games have been discontinued. Plus, the GTS systems are different so you so you wouldn't be able to anyway.