Stupid question. Is it possible to go back to fort condor and play that minigame? I've never been able to, but some guy told me you can. I think he's bullshitting. So is it possible or no?

You can play it up until the Huge Materia Quest. Apathetic Aardvark's FAQ on gamefaqs is really detailed on it.

Yeah as Teknoblade said it is possible to go back and do it.

Alhough if you are away for a long time they get broked and complain about wanting more money the greedy bastards