Can an employer use a mandatory retirement age for workers who are not employees?
No, if the contract of a worker is terminated on reaching a certain age, regardless of what that age is, the worker will be able to argue that they have suffered direct age discrimination. The employer will need to be able to justify the termination objectively if it is to avoid liability, ie by asserting that the termination on age grounds was a proportionate means of achieving a legitimate aim. A worker who is not an employee (for example an independent contractor, agency worker or partner) will not, however, be able to claim unfair dismissal, because that claim depends on the individual being an "employee".
Following the removal of the default retirement age, employers must also be able to justify objectively a mandatory retirement age for employees, if they retain one.