Set a retention policy on the bucket with a period of 7 years.

Use IAM Conditions to provide access to objects 7 years after the object creation date.

Enable Object Versioning to prevent objects from being accidentally deleted for 7 years after object creation.

Create an object lifecycle policy on the bucket that moves objects from Standard Storage to Archive Storage after 3 years.

Implement a Cloud Function that checks the age of each object in the bucket and moves the objects older than 3 years to a second bucket with the Archive Storage class. Use Cloud Scheduler to trigger the Cloud Function on a daily schedule.