Robin - I called them just yesterday. I have a 12 year old with Down Syndrome, and just booked a cruise for next year. He will be 13 by then, so I was afraid they wouldn't let me put him in the 8-12 program. There is no way he'd be ready to be with the teens.
Anyway, they told me that you could "downgrade" age groups, but could not "upgrade" (they can't go with the older group). But he did say "as long as he doesn't need one-on-one attention." So it sounds to me like you have your choice of the 0-3 or 4-7 age groups, but they won't give special attention.
LisaB