We are a family of 5, and we went to Ireland last year with ABD. Kids were 8(turned on his birthday, it was the best day of his life. ABD had surprises every hour or so...fantastic!),10, and 13. We had connecting rooms in all 3 of our hotels. Just opened the door, no problem, almost like the same room.
I thought that 7 was a fine age for this particular adventure. I actually think 12 is getting kind of old. We had 28 people, 13 kids, ages 7-15, 15 adults.
Other families didn't always get connecting rooms, but ABD certainly tried to accomodate them. I wonder if we were so lucky because we were the first people booked on the tour!
It was the best tour possible for families of younger kids. I wouldn't even consider another company for kids under 10
Good luck. It was a wonderful experience.
PS All our hotel rooms in Ireland were massive!