Auto delete contacts in user's account

We would like the ability to auto delete contacts in user’s accounts based on a lapsed timeframe or some other criteria.
The reason for this is that when an envelope is created the contact will be stored automatically in the user’s address book and stay there until the user manually removes it.  How compliant this is with UK and EU GDPR is concerning.  We would like an ability to automatically delete contacts after e.g. 6 months of last use.  We would like an ability to favourite contacts so they are not deleted where maybe we will be working with them again in the future but maybe outside of the 6 month timeframe.