I'm not a lawyer, but that smells of illegal discrimination to me. It is absolutely inappropriate for an interviewer to initiate a discussion on an applicant's age. Have you considered contacting the dean of admissions at the school or filing a complaint with ADEA?
A couple possible answers (out of many) off the top of my head:
1) I would first ask the patient why they would like the amalgam to be removed. If I learn that the patient is making the request based on false information (from Dr. Oz, investigative reporting, etc.) about the safety of amalgam, then it is my professional responsibility to explain that scientific research does not corroborate their belief. This is based on the legal/ethical concept of "informed consent."
2) I would refuse to do the procedure if the patient were pregnant because research shows that patients can potentially ingest a relatively high dose of mercury during the removal of amalgam fillings, and mercury is a teratogenic neurotoxin.
3) Removal of amalgam fillings requires drilling into the tooth structure surrounding the restoration, so if the procedure is not dentally necessary, this would be in violation of the modern principle of "minimally invasive dentistry."
4) From a utilitarian perspective, it is more ethical to refuse to treat one patient than to risk losing your license to treat thousands of other patients.