Sorry, but a credit card is the only form of verification that a person is 18 years old or older which eBay accepts, and is needed to buy your item, or any bladed item. Anyone of any age, can own a debit card.
The only workaround, is to perhaps ask a family member or friend, who does have a credit card on their eBay account, to buy this item for you.
@stelgeo.2