Pokemon Black Help

I'm in that forest where you went through all those Plasma grunts to get the skull back and I came across this little old man. I happened to have my dousing machine turned on at the time and according to it I have to go down those stairs he's standing at the top of. Could somebody please tell me how to get that bald headed rock to move?

you have to beat the game and then he will let you pass

What?! No way! Oh man! Thanx, I think.