Currently government employees can continue to work well past retirement age. In most cases employees who continue to work provide excellent service and a wealth of insight through their experience. However, some become, essentially, "retired in place". In these cases, the burden of proof of an ineffective employee falls on the supervisor. Often, the time and effort it takes to provide such proof is significant and managers will opt not to invest the time. So, the employee stays on the payroll with little contribution to the organization.
The idea would be to consider, at some number of years past retirement eligibility (say 5?), the continuation of that employee is subject to the approval of the supervisor. And that this approval or disapproval was simply left up to the supervisor and could include consideration of workforce planning as well as past performance.