Dear Ms. Park,
Thank you for posting your request on History Hub!
Under Federal Aviation Administration (FAA) Record Control Schedule Registry Modernization System: Airman Certification Records (N1-237-06-001), original papers records relating to private pilot certifications (popularly known as private pilot licenses) are destroyed after making a microfilm copy, and the microfilm copy is destroyed after 60 years or when no longer needed, whichever is later. If these records still exist, they are in the custody of the FAA. Please contact the Airmen Certification Branch to inquire about these records.
Additionally, you may wish to search the FAA’s Airmen Inquiry database, although the website does not state the date span covered by the database.
We hope this is helpful. Best of luck with your research!