Actually, an 8 year old can get a female pregnant, just as an 8 year old girl can get pregnant, it's just rare. Did you happen to see the size of the Little League Players in the playoffs over the weekend?
He says he's not the father, but legally, it may not matter. The mother likely just picked a name and got a default order, as is quite common. Once the order is in place, it has to be paid, whether he's the father or not, in 20 states. In the other states, there's a 24 month limit to file a challenge, and this girl is already 11 years old. If they allow him to get out of the order, they would be opening a major can of worms they are not ready to handle with 30% of men paying child support learning they are not the father. Women's groups have been pouring money into opposing men being allowed to get out of these orders. They managed to stop the effort to pass the law in Kansas in January, but in June, Missouri passed it with the 24 month limit.
Regardless of his age, or paternity, he will have to pay.