Are children allowed on the regular Rick Steves tours?
Children 8 and older can go on Family and My Way tours, and teenagers can go on any tour. See the tour FAQ page, under family tours https://www.ricksteves.com/travel-help/tours-faq
I have been on tours with teens in the past. It is important to realize that they could be the only teens on the tour. They should be able to relate to and get along with adults that are older. That said, it was always a joy to have the teens on the tours.
My biggest concern would be the tremendous cost of bringing an entire family on a tour. If it fits your budget and your interests, go for it.