It doesn't matter if he'll be 31 next year.
Makelele is much older and he still brings the stability in midfield noone else in the world does.
The thing about players like Emo is that my eye and another non-expert's eye can't see what is he capable of and how useful he is. But all the greatest managers in the world can't even imagine their teams without players like Emerson.
As someone allready mentioned, Emerson does the work of 3 man. He may not driblle the entire opponents defense and score many goals, but he'll certanly stop many opponents actions before they even begin and create a chance for us that way.
Did you see Brazil without Emerson against France at the WC ? Zidane did whatever he wanted , while super stars like Kaka and Ronaldinho couldn't even try to do smthg with Makelele-Vieira in front of them.
We need such players, and there are only 3-4 players like Emo out there. We can't buy Makelele, Vieira, Gattuso or Diarra. But we can get Emerson back, and we should do it.
P.S : I never liked him though.
