Peter Clemens said in his pension affidavit that the was sixty years old (In December, 1820), that he was living in Union County, PA with his wife Elizabeth who was 58, and their daughter Mena who was 13. His pension application is available on Fold3 (a pay site, but many libraries have subscriptions) and would probably be worth reading to see if there is information that would clarify whether or not he is your ancestor. The application should tell you where he lived when he enlisted, what unit he was in, who his officers were, and what actions he participated in. Many list all the places the person has lived, some list family members. There are also often affidavits from neighbors or other men who served with the person.