Can I send money to someone in another country

The short answer is no - you must be 18 years old and a US resident. But let me explain why.

There are three payment methods inside Apple's Wallet: Apple Pay, Apple Card and Apple Cash. They are all distinct and their different functions can easily be confused.

Apple Cash is the "peer-to-peer" part of the digital wallet that I believe you are referring to. Apple refers to it as a "prepaid debit card". It works through iMessage which means both parties must have iPhones and be signed in with their Apple ID. To the best of my knowledge it is not licensed as an international money transfer service - thus the requirement to be a US resident.

Being retired, we have homes near our families in both Brazil and the US. Until a few years ago we were stuck using the familiar "SWIFT" system of wire transfers, which does not function well in Brazil. Now we use Wise (formerly TransferWise) to move money. Much cheaper than the alternatives. It is particularly popular with university students studying overseas, which tells you that it is an inexpensive/safe/convenient way to move small (and in our case larger) sums of money.

Hope this helps.