Start now if you have time. Many guilds recruit or reorganize now in anticipation of WoD and you can practice, meet some people and get much needed experience now, when content is nerfed and on farm. Much harder for completely new people to get accepted on progress.
It's unlikely that WoD is right around the corner, so you probably have a few months. I'd say go for it. You probably won't get farther than normals, but you might end up finding a home to raid in for WoD. Even if you don't, having the experience will help you find a spot in WoD.
Also consider that raiding isn't something you pick up in a week if you've never done much before or if it's been awhile. Learning the encounters, the rotation, getting your ui the way you want it definitely takes more than a week or two to get it fluid.