Depends on everybodys view of world class, I've got some very good players on a Free - Felipe Melo, Joe Cole (though he was 32) etc but never any of the top 5/6 players no
As tubby said, it depends on what you consider world class. I've signed Rooney, Messi, C Ronaldo, Deco, Dzeko, Adler, Akinfeev, Balotelli, Lahm and others on free transfers but the first four have all been over 30 when I signed them.
i got mascherano and de gea for Juventus, Hulk for Arsenal, Rooney for Real madrid, Cristiano Ronaldo and Ivica Olic for Sporting CP. De Gea was a massive signing, since my keeper at juve sucked.