Like Josh said, sign up. Just don't make any long term commitments.
Do it now. If they have a good program, they will ramp you up slowly. Your job is to make sure you pace yourself and don't let your ego get the best of you (yet).
If they run you into the ground and beat you up for the first few weeks. . . it might not be the best place to train. Without committing, you should be able to walk away at any time.