Helen, Joan and I were 65 when we got our yellow fever vaccination‘s. Other than minor arm soreness at the injection site, there were no side effects. if you decide to get a waiver, it appears that your doctor must fill out the appropriate section of the yellow card as well as providing a waiver letter. Here’s the language from the CDC site:

“If you cannot get yellow fever vaccine for medical reasons and you are traveling to a country with a yellow fever vaccination entry requirement, your doctor will need to fill out the Medical Contraindications to Vaccination section of your yellow card. In addition, your doctor should give you a waiver letter. If you plan to use a waiver, you can contact the embassies of countries you plan to visit for more information.”