Cruise vacations are as popular as they’ve ever been, and a surprising reason why is rising interest from a fickle group that’s historically shunned the geriatric-focused industry: young travelers.

Look at Royal Caribbean Cruise Ltd., where half of the company’s passengers are Millennials or Generation Z, according to Chief Executive Officer Jason Liberty, and the fastest growing portion of its customer base. Other cruise lines are seeing similar youthful growth, with the average age of cruise passengers falling for two straight years after being largely stagnant since at least 2016, according to the Cruise Lines International Association.