I believe there are two factors contributing to the perceived rise:
1. The US has lagged behind Europe significantly in their knowledge and diagnosis of celiacs disease/intolerance, so more people are finally being diagnosed.
2. The wheat in the US today is significantly different from the majority of European wheat [1]
This is purely anecdotal, but I (22) know a lot of people in my generation who easily get stomach aches from milk and gluten. I've had some problems myself. Really kinda sucks.