i'm not entirely clear on what you mean by the root mass.
to divide an ornamental you'll need shovels, pitchforks, sawzall or some sort of saw and a strong back. dig up your grass or at least dig around the sides so you can get to it. saw it into sections, from the crown down through the roots. the divisions really depend on how big you want them. the smaller they are the longer they take to get big enough to make any sort of impact. usually when i divide i leave the clumps about 6-8 inches around. personally with yours i would wait another year to divide it, but it could be divided in half at this point. what kind of grass is it?

It is pink pampas and very young. The root mass is only about 6" wide. Should I plant and wait till next year?

you could divide it now, but you'll end up setting it back. i would plant it now and then maybe in two years divide it.

Thank you for the advice cody!