content: Statutes of limitations are common throughout the law. Why can't you be prosecuted five years after committing a felony? Why can't you sue for a breach of contract more than four years after the breach? Among other things, it's not fair to make someone try to defend a claim years after the fact. Imagine if the guy waited until the kid turned 18 then asked for a refund of the tens of thousands in child support he paid. It's not fair to the kid because the opportunity to find the biological father may have been lost, and it's not fair to the biological father who has no idea there is a kid out there and he's now responsible for back child support.