Criminal Law Questions? Ask a Criminal Lawyer.
It is too late to appeal. There is a very short window to appeal (60 days). Even if you could appeal, it is next to impossible to overturn a conviction where you plead out. Since you will have been on the transcript agreeing to a factual basis, it is hard to argue it.
That said, if there are extenuating circumstances, you might be able to get somewhere with an application for a pardon and clemency. That is your only hope for a conviction so old.
You can dowlaod an application for pardon here: