Hello, j4k0bnp
In both case scenarios of buying you can also explain that seller lied about his/her age and that is the reason you are in this situation.
If you paid as service it should be easy, just go to activity then go to transaction and there should appear chargeback option or something similar under details and total of the payment. You provide what happened, or like "didn't get what I paid for" or something like that and after If I don't mistaken you will automatically get your money back as seller hasn't provided any information.
If you paid as friends and family its a lot harder, you can try to contact paypal support, and they might help(not high chances because you did F&F)
(ONLY IF you paid with paypal using your credit card) (warning this option is not recommended but might help as banks, usually in EU region are helpful in all kinds of situations)
if that doesn't help you can try to contact your bank and explain the situation and they might help.(If you paid with paypal using your credit card)(Warning: If you do this and they do charge back your bank account might be blacklisted from PayPal or your paypal account get deleted)
If this helped I would appreciate Kudo if you have any other questions Reply to this message and if i notice it I can try to answer them : )
