Elle, I don't know what Robb Wolf said, but I'll see if I can fill in some answers for you. :)
One of the mainstays of the Paleo approach to eating is to avoid excess fructose. There are lists showing of the amount of fructose in fruit, relative to glucose. Some try to eat only fruit that has an equal amount of fructose and glucose.
Fruit is also what is called a fast-acting carbohydrate. That means it raises the blood sugar more quickly, or to a higher level, than slow-acting carbohydrate. If a person has normal blood sugars, a healthy pancreas, etc., this is not a problem. If a person has diabetes, or some other kind of abnormal blood sugar regulation, then limiting or avoiding fruit helps normalize blood sugar, and to maintain normal blood sugar. Dr. Richard Bernstein explains the science of this in a way that is very easy to understand. Here is a page at his site on what foods to avoid, due to their raising blood sugars too much.
There is a great deal of interesting information on nutrition at his site. :)
ETA: To add to what Jasmine posted about it not being good for weight loss, if one eats too much of it. Eating carbohydrate raises the blood sugar, which tells the body to produce more insulin to keep the blood sugar at a constant level. More insulin means that more fat gets stored. For someone who is at a healthy weight, with normal blood sugar regulation, this is not problematic. For someone who needs the fat to come out of storage, having lower insulin levels helps. Less carbohydrate means less insulin. Dr. Bernstein explains the science of carbohydrate, blood sugar, insulin, fat storage, etc., at his site, and in his books.
As to how much fruit you can eat and not have it cause you any trouble:
No one on the internet can tell you this. It depends on how your body uses what you eat.
If you are tracking the amounts of carbohydrates you eat, here is the USDA food list site, and here is another source at a Low Carb tool site, for checking amounts.
As Jasmine posted, we are all different. It takes experimenting, for some of us, measuring, and for some, testing blood sugars with a glucose meter, to determine how much of what one can safely eat.
Hope this helps some. :)