I found the link but It was on the Carnival Cruise line forum I believe RCCL have a similar policy:
At it said on the post:
"Effective January 1, 2008 for new bookings only.
Infants must be at least six (6) months of age at the beginning of the cruise.
For Transatlantic, Hawaii and South America cruises only, infants must be at least twelve (12) months of age at the beginning of the cruise."
As nickol also states on the post RCCL policy is:
"Their cruise policy states that no infants under 6 months old are allowed to cruise to Alaska."
That was why I assume that the limit for traveling with kids was 6 months or older
Sorry my mistake
Nickol I recomend you check this post I don't think is a good idea to cruise with an infant and on the link you can find out why.