as provided on Google: https://support.google.com/analytics/answer/7667196?hl=en
The Google Analytics Data Retention controls give you the ability to set the amount of time before user-level and event-level data stored by Google Analytics is automatically deleted from Analytics’ servers.
These settings will not take effect until May 25, 2018.
User and event data retention
The retention period applies to user-level and event-level data associated with cookies, user-identifiers (e.g., User-ID) and advertising identifiers (e.g., DoubleClick cookies, Android’s Advertising ID, Apple’s Identifier for Advertisers).
Keep in mind that standard aggregated Google Analytics reporting is not affected. The user and event data managed by this setting is needed only when you use certain advanced features like applying custom segments to reports or creating unusual custom reports.
You can choose how long Analytics retains data before automatically deleting it:
- 14 months
- 26 months
- 38 months
- 50 months
- Do not automatically expire
When data reaches the end of the retention period, it is deleted automatically on a monthly basis.
If you change the retention period, then any affected data is deleted during the next monthly process. For example, if you change from 26 months to 14 months, then any data older than 14 months is deleted during the next monthly process.
Whenever you modify the retention period, Analytics waits 24 hours before implementing the change. During this 24-hour period, you can revert your change and your data will be unaffected.