I have received a 20 Euro PayPal balance. I want to buy a game but when I scan this QR code I have to enter my credit card and so on. Is there a way to use the credit?
To pay in PSN with PayPal, you have to provide an ID or passport, not a credit card. You simply select PayPal in the shopping cart, log in if you haven't already done so and after you have given your ID / passport you can buy the game.
I'm directed to the PayPal site where I have to enter my credit card number to complete the purchase
That comes from PayPal. This is to check if you are really 18. If you are a minor, your account will be blocked and you will never be allowed to use PayPal again.
Could I work around it by creating a new account and transferring the money there?
Maybe for a short time.