Complicated Issue

What is the name of your state? Oregon

I may or may not be the father of a girl who is about to turn 18. There is another person listed on the Birth certificate due to the child being the result of an affair with a married woman and I have never been contacted to pay support. I was 15 at the time of conception and have taken no active role in parenting and honestly don't know if the girl is aware of my possible biological role. I now have 3 legitimate daughters of my own and no interest in adding to my financial burden. I would however like to offer this girl the option of a blood test and if she is biologically mine I would like to offer her knowledge of her sisters (and me). My question is, when can I approach her without having to worry about child support obligations or the government coming after me to pay for back AFDC payments? Thanks.

What makes you think it's a good idea to rock this kid's world? You couldn't be bothered for 18 years, why now?

I'm just wanting to give her the option to know that she may have several younger siblings and my guess is that she is at least aware of the possibility of my paternity.

Then I'd suggest you speak with her mother first.

I respect that you have feelings on the "should" or "should not" piece of the issue but I honestly have had many years to think about if and when I should approach this and I'm still undecided. It is not my intention however to solicit advice regarding that particular conundrum. My questions are:
1) What may or may not be my LEGAL child support obligations on an 18 year old who has a different father listed on her Birth certificate?
2) What are the statute of Limitations on both the government (AFDC payments) and the mother asking for support and/or back support?