Personal data processed for any purpose must not be kept for longer than is necessary for that purpose. Once the purpose for collecting the data has passed, you need to consider if there is a reason for you to retain that data.
Data protection legislation does permit personal data to be stored for longer periods if, subject to the implementation of appropriate safeguards, the data will be processed solely for:
archiving purposes in the public interest
scientific purposes
historical purposes
statistical purposes
Examples might include old electoral registers held to determine the eligibility of overseas applicants, or election results.
You should practice data minimisation – don’t ask for, and process, personal data if you don’t need it. For every document you possess, ask yourself “for what reason am I keeping this document?”