I do have a slight prejudice against older ships myself, but find myself booked for 12 nights on Millenium and 10 on Summit in the next 18 months, so hope my preconceptions and some comments on this thread do not come to fruition.
I was on a 13 year old NCL ship that was maintained appallingly, rust, dirty decks, battered cabin, mouldy grouting etc.
The Revolution of Millenium and Summit is welcome, but I am expecting if I look in the corners the age and condition of the ships will be more evident.