The age rules that matter are the Korean ones. Participants born after December 31, 2008 count as minors under Korean law and must be accompanied by a designated responsible adult throughout, with a consent form, and may not drink or smoke. Organizer-provided accommodation is open only to participants born on or before July 31, 2013, so a child under about 14 cannot use group lodging; families with young children are told to pick a package without accommodation. Volunteers must have been born on or before December 31, 2008. The earlier page on minors at WYD Seoul covers safeguarding and chaperone rules.
No one is excluded for being older. Youth ministers, parents, grandparents, religious and clergy register in the same system, and the catecheses and main events are for everyone registered; a 45-year-old chaperone receives the same package. Registered priests give their availability for the Reconciliation Park. Being Catholic is not a condition of registration, though the week is built around Mass, confession and the Vigil.
The standard registration route for Americans is the official Seoul 2027 site only; the USCCB states that plainly and handles bishops separately. Registration was announced for late October 2026. Beyond the forms, the real requirement is physical: a week of walking in August heat, a night outdoors at the Vigil and a sleeping bag on a gym floor, which is why U.S. dioceses advertise it to young adults and ask older pilgrims to judge their fitness honestly.