It looks amazing and I would love to go but the whole point of group travel, at least for our family, is companions for our son. I've only been on 1 ABD but it seems that the trips skew toward the younger side. Were there any/many teens on this trip?
This particular cruise had ~150 guests and 20-25 kids. There were around 5-10 teens.
Each cruise varies. You could ask a Vacationista for the number and ages of the kids on the particular cruise you are considering.
Given the much larger size of a cruise compared with a normal land-based ABD, I would expect the odds of having other teens would be higher on a river cruise.
A note about teens and activities: Since parents could not leave children behind on the ship during excursions, I saw kids in wine tasting events. Non alcoholic drinks were available but the venue also allowed teens to drink, if the parents gave permission. They also allowed teens in the nominally "adult only" Chef's Table.