How do we cater for age change in an unrestricted event like pension?

Summary:

We have a requirement from the client whereby a Pension plan requires that the employer contribution is based on the age of the employee.

Content (required):

Hello

We have a requirement from the client whereby a Pension plan requires that the employer contribution is based on the age of the employee.

Currently we have created an unrestricted enrollment on the plan having one option in it. The enrollment method is set to Explicit, Default Enrollment Rule set to New - default; current - same enrollment and rates and Enrollment Rule  set to Current - can keep or choose; new - can choose.