Royal Caribbean is one of the most popular cruise lines in the world, and it has a strict policy regarding the minimum age for babies on board. According to Royal Caribbean, babies must be at least six months old on or before the first day of the cruise. If your baby is younger than six months old at the time of departure, they will not be allowed to board the ship, so plan to bring a copy of their birth certificate. This policy is in place to ensure that all passengers are safe and comfortable during their voyage.