Perhaps you should ask the seller if they ship to an unverified PayPal account first. Otherwise you may be wasting your time and theirs. If you have never verified your PayPal account with a REAL credit card or checking account many sellers will not ship to you.

Under 18s can't use ebay...

You can't use prepaid credit cards on eBay.

I want to buy something on Ebay right now but I want to go to the store and a pre-paid credit card tomorrow. How can I buy it now but pay it in a 1 day or 2? The seller says that he will give me 5 days to pay for the item before opening an "unpiad" case.