This is an issue which falls only partly within my remit.
Fees for a driving licence application are set in Regulations for which I am responsible, and the Regulations state that fee is waived in the case of applicants over 70 years of age.
The requirement to have tests for medical fitness for older applicants has been in place since 1964. It is a prudent measure and reflects wide-spread international practice. Age-related deteriorations can impact on people's ability to drive, often without the person themselves being fully aware of it.
The cost of medical tests is unfortunately not within my remit.