It could be that they paid by E-Check, which can take several days to clear.
It could also be that your new to selling. I am only going to assume that because you said it was the first item you have sold on Ebay. Paypal now holds your funds for up to 21 days. They want to make sure that there are no problems with your order, such as a dispute, claim, return, or a chargeback. After they determine that the order was fulfilled and the customer is satisfied, they will release your funds.