A prepaid card isn't a credit card. Payment processors can tell the difference between card types. You have to be 18 or older to get a credit card issued in your name (although you can add an underage authorized user to your card). And there are now other requirements needed if you're under 21 in the US, such as proof of income or a cosigner.

A prepaid card is also not a debit card (debit cards are attached to a bank account). To get a debit card you must be either 18 or have a legal guardian who is at least 18 on the account.

I don't about the US or Australia, but this is definitely not true everywhere.

I know for a fact that in some countries children as young as 13 can have bank accounts and debit cards that are not linked to a guardian.

Not necessarily. You can be issued a debit card from age 11 in the UK, although it will only do online transactions to prevent the account going overdrawn.

Allowing a parent/guardian control of the account is optional.

https://www.moneysavingexpert.com/banking/cards-for-under-18...

But the discussion was around being able to use a credit card to verify that you're over the age of 18. My point being is that a credit card doesn't have a photo to verify that you are who the persons name is on the card.