Apple Pay - From which age?

See the following from Set up Apple Pay - Apple Support

Apple Pay isn't available for children under 13. Age varies by country or region.

Also, to send or receive money via iMessage, see the following from Send, receive, and request money with Apple Pay - Apple Support

To send and receive money with Apple Pay, you must be at least 18 years old and a resident of the United States.

It is the same according to https://support.apple.com/fr-be/HT204506

Apple Pay n’est pas disponible pour les enfants âgés de moins de 13 ans. L’âge limite varie selon le pays ou la région.