For Apple Pay, see the following footnote from Set up Apple Pay - Apple Support
If you're less than 13 years old, Apple Pay isn't available and you can't add a card in the Wallet app. Age varies by country or region.
For Apple Cash, see the following from Set up Apple Cash - Apple Support
Be at least 18 years old and live in the United States.
Except for Set up and use Apple Cash Family - Apple Support
You can set up Apple Cash for the children and teens in your Family Sharing group so they can make purchases, and send and receive money in Messages. You can even limit who your child can send money to, get notified when they make transactions, and lock their account.1
and
How children and teens can use Apple Cash
If your family organizer set up Apple Cash for you, you can use it to make purchases in participating stores, apps, and websites.
You can also use Apple Cash to send and receive money in Messages with Apple Pay. If you're less than 13 years old, you can't add a card to Wallet to use with Apple Pay.
