More and more people are being exposed to the internet, which in turn exposes them to the plethora of gambling sites available.
I suspect that it's having an even bigger effect on adults over 40 who use the computer, I've seen some completely gullible ones in my time.
I would say that there would be a clear correlation between time spent online and risk of gambling addiction, since younger people tend to spend more time online than the older generation you are probably more likely to see it in the young. That doesn't mean that being young is the risk factor, as correlation doesn't equal causation.