The age limit is 19, 2007 was the first draft that had this rule. Here is the projection: http://www.nbadraft.net/index.asp?content=mock2009
the rankings are based off of this year, but this is just to give you an idea of where the future is projected to be drafted. I would hope Rubio will stay for at least 4 or so years, but I think he'll be in the NBA by the time he turns 20. Maybe if Rudy stays then Ricky also will. But the best time for Rudy to come to Portland would be for the next season, because they could really use someone like him.