Between 2 trips there with my kids an my nieces we have seen HDD through the eyes of an 8mo, 3.5yo, 7yo, 11yo, 2.5, yo, 5.5yo, 9yo, and 12 yo. Both times all the kids at all the ages loved it(well, 8mo slept). Even DS who was in a mood that night could not keep a straight face as hard as he tried.
On the other end of the spectrum, my father who was 60 at the time had a blast, as did the rest of us in between. I think it appeals to all ages.