Royal Caribbean is starting to go broader with its vaccine mandate.The world’s largest cruise line on Friday said all U.S. passengers ages 12 and older will need to show proof of a COVID-19 vaccine to cruise with the line in Alaska starting on Aug. 1.Even before Aug. 1, only fully vaccinated passengers over the age of 16 will be allowed to sail on Royal Caribbean voyages in Alaska.For more cruise news, reviews and tips, sign up for TPG’s new cruise newsletter.Both of the age cut-offs are lower than the line had previously announced for sailings starting up soon in the Caribbean and the Mediterranean.On those voyages, the line had announced that all passengers ages 18 and older would need to show proof of a COVID-19 vaccine to cruise.It’s not clear whether the new age cut-offs just apply to upcoming Alaska sailings or the Caribbean and Mediterranean sailings, too. A spokesperson for Royal Caribbean did not immediately respond to questions about the topic from TPG.As of late Friday, Royal Caribbean’s website still listed 18 as the cut-off age for a vaccine requirement on Royal Caribbean sailings.The new age cut-offs for Royal Caribbean sailings in Alaska were disclosed as part of an announcement Friday that the line and sister brand Celebrity Cruises planned to restart cruises to Alaska in July. The announcement was made by Royal Caribbean Group, the parent company of both Royal Caribbean and Celebrity.Sign up for our daily newsletterEmail addressSign upI would like to subscribe to The Points Guy newsletters and special email promotions. The Points Guy will not share or sell your email. See privacy policy.The same age cut-offs announced for Royal Caribbean cruises in Alaska also will apply to Celebrity sailings in Alaska, the announcement said.Celebrity already had dropped its age cut-off for mandatory vaccines for summer cruises last week from 18 to 16.A growing number of cruise lines have announced they will require all or most passengers to show proof of a COVID-19 vaccine to cruise on at least some of their ships in the coming months.In some cases, cruise lines are requiring all passengers to be fully vaccinated for COVID-19. In other cases, cruise lines only are requiring adults to be fully vaccinated.Cruise lines that have announced a COVID-19 vaccine requirement for all or at least some upcoming cruises include Carnival Cruise Line, Celebrity Cruises, Crystal Cruises, Cunard Line, Disney Cruise Line, Holland America, Norwegian Cruise Line, Oceania Cruises, Princess Cruises, Regent Seven Seas Cruises, Royal Caribbean, Silversea, Virgin Voyages and Windstar Cruises.Lines that are restarting operations without requiring passengers to show proof of a COVID-19 vaccine include MSC Cruises, Uniworld Boutique River Cruise Collection, and German lines TUI Cruises and Hapag-Lloyd Cruises.Planning a cruise? Start with these stories:The 5 most desirable cabin locations on any cruise shipThe 8 worst cabin locations on any cruise shipA quick guide to the most popular cruise lines21 tips and tricks that will make your cruise go smoothly15 ways cruisers waste money12 best cruises for people who never want to grow upWhat to pack for your first cruise