You need to speak with a Tax Attorney. The FTB has a 20 year statute of limitations on debt collection. However, the time may not start running until the debt has discovered by the FTB.
It seems difficult to believe that you would have liability for something that occurred over 20 years ago and you are just finding out about it now. I suppose anything is possible. So either you must get on the phone with the FTB and solve this, or you need some CPA or tax attorney to get to the bottom of this on your behalf. The FTB may seek to put a lien on your assets or wages if you don't get right on it. If the liability is now up to $8,000, then it is time to hire someone like us (there are many other fine tax lawyers on AVVO as well) to work on it.