He is giving his opinion, as a politician, about how he feels. I think his 99% is supposed to be taken in the manner it was quite obviously - to me - intended - to mean "a vast majority". He is saying he is shocked by the young ages of the girls, and that people who dismiss concerns by saying it's the oldest profession in the world need to bear in mind factors such as history of abuse, current abuse, coercion, being young and vulnerable and so on. He is not saying he has carried out an extensive scientific study and these are his findings, nor is he saying he has spent a period of time combining peer assessed scientific studies and now he is presenting the results. He is a normal person using standard vernacular to emphasise his point.
If it makes people understand better, try replacing the "99%" with "most" or "many" or "lots" or some other term like that.