Yes, they were on board. You have to get a special appt time to see them, but they do spend lots of time with you, sign things and take pics with you. Just got off Wonder this morning.
They gave us as many tickets as were in our stateroom. I would assume they would welcome any age. We had three adults and a 17 year old and no one batted an eye. And the princesses spent lots of time with us and took as many pictures as we wanted. Not rushed at all. They give you a time to arrive and sit you down with coloring pages. We sat for about 3 minutes before being directed to the line, which was very short. We were in and out in about 10-12 minutes.