River cruises aren't that popular among the younger people. They tend to attract only the baby boomers and retirees. That is changing with some river cruise lines targeting the younger generation with tours that appeal to them.
For example, the river cruise brand Avalon Waterways offers "Active & Discovery" cruise which focuses on active excursions and tours that appeal to the younger river cruisers looking for deeper cultural immersions.
Should you be considering a river cruise, you may want to check out this article that gives tips on how to find the best river cruise liner and six ways to cut down on your cruising costs.