In OH, if I remember correctly, you have to prove (yes, you have to prove) that you are not the father before the baby's first birthday. If you don't, then even if it comes out later that he's not your child, you still have to pay child support. How do I know? My brother-in-law's ex, while living with the man she left him for, sent him a nice child support letter 1 week after "his" child's first birthday.