In large part, the answer depends on the jurisdiction. I've never heard of such a case in Illinois, although I suppose it's technically possible. One defense should be that you had no knowledge of the child. Run, don't walk, to an attorney who specializes in family law in the jurisdiction where this case has been filed.
No. In some states they may enforce retroactive support or support for while the "child" attends a 4 year university. Retroactive support is generally only backdated 2 years from notice.
There is no statute of limitations on unpaid child support.
Not likely.
what do I do if my child's father is no where to be found what do I do if my child's father is no where to be found
No.
Yes, and it can be increased, but you can ask it to be reduced or stopped using a rebuttable presumption argument. see link
There is no statue of limitation in California on child support but it's usually not more than 18 years unless the child support agreement says differently. Your child is not a child and has not been for many years so I don't know why you are still paying and why you have found it acceptable to do so for so long. You need to read the agreement you signed and if this is not correct that you are still paying, you need to contact a lawyer and get the money back from the child's mother. If it is correct and you want to end it you have to go to court so the judge can end it.
There is no statute of limitations on collecting past-due child support.
until age 19
Depends on what your decree says. In most cases, child support is paid until the child reaches 18 years of age or when the child graduates high school, which ever comes first.
see links
Yes. If paternity has been established the father will be required to pay child support until the child is at least eighteen.