Agree with pp02_diver.
I took the class with about 20 dives. I was fortunate enough to have some experience with GUE and DIR prior to taking it, which helped, but I didn't come CLOSE to passing, nor should I. It was hugely educational for me.
The only drawbacks to taking it so early, was that my buoyancy wasn't solid. I don't mean DIR-F solid, I mean just recreationally solid. I was doing ok with my diving, but the idea of staying still in the water was Jedi stuff. Unfortunately with DIR-F, you really do need to have reasonable buoyancy and control of yourself. Otherwise you miss out on some things.
Take the class, forget about passing, and just absorb as much as you can. Then do 50-100 dives and take it again and see if you can pass.