We just got back from Enchanted China. Our trip was about half adults and half children (under 25 years old). The age range of adults was from about 40-55. At one of our hotels, we happened to overlap with a Tauck tour. I've seen Tauck compared to
ABD. The age range of the people getting on that bus was about 50-75.
The family friendliness of the tour comes from the overall friendliness and upbeat style of the guides as well as the "active" nature of the trip. There is more walking than I would expect on a tour geared for older folks. At one of our hotels, we spent a fair bit of time bike riding. A few of the activities were geared more towards the kids, but they weren't really childish. At one stop, we painted ceramic figures. At another stop, we learned how to make Chinese noodles and see a demonstration of glassblowing.
I liked the ABD tour immensely because of the guides, my fellow travelers and the style of the trip. If I had gone on a trip where we spent hours on buses and listened to a guide drone on about history and artwork, I would have hated it. The ABD tour was geared more towards learning about the people and the contemporary culture.
One night, they had a junior adventurer dinner and movie. I think most of the adults ended up at the movie too.
Overall, I would say that rather than saying that the ABD tours are aimed at families with children, I would say that they are aimed at the 55 and under age group.