Is there a statute of limitations for payment of child support after 25 years if no court order was issued and paternity was not pursued by the mother

It depends on your situation.  If a child support obligation/order has existed for 25 years, each past due child support payment becomes an enforceable judgment, meaning you can collect it, plus interest, and can usually collect your costs incurred by having to go after it.  Child Support Enforcement can also help you free of charge.  If no child support obligation existed, you are most likely out of luck.  Child support cannot be modified retroactively; therefore, if there was no order, you can only obtain child support from the time you file to receive it.  However, child support terminates by law when the child reaches 19, so you cannot file to receive a new child support payment once the child is 19.  Paternity is not required to be proven before collecting child support.  The father has the right to request a paternity test if he chooses.  In essence, it is a defense, not a burden on you.  I suggest you consult an attorney regarding your situation.