He will be able to do everything, it will just all take more time. Check-in will require that he wait in a longer line and he won’t be able to carry out many activities onboard without waiting in lines or on the phone. Those who use the app can make, cancel or change dinner reservations, purchase photos, book shore excursions, ask questions of guest services etc using their phone wherever and whenever they like while on the ship. He will simply have to go do those things in person or go use the phone in his cabin. If that’s his preference, it will work