Without more specific facts surrounding your case, generally under 42PaCSA 5553, proceeding for a summary offense under the vehicle code must be commenced within 30 days of the commission of the offense. You have 10 days to respond to the citation with the court. I suggest that you contact an experienced traffic attorney asap.
Mr. Keller offers good advice. If you had an attorney representing you on your current case, talk to them first. If you were not represented, find an experienced lawyer familiar with the court system in Delaware County.
My colleagues are correct. Your only recourse is a Governor's pardon and not easy to get. My sense of it is, that even though the conviction was in 1992, you may need a more compelling reason than the wish to purchase a firearm.
I agree with both of my colleagues. First get an experienced attorrney. The statute of limitaions is not necessarily absolute and there are numerous factors that can determine whether or not the statute has run. Good luck.