For what it's worth: For our recent trip to Brazil (up the Amazon), I took the YF vaccine at age 64, after conferring with my doctor. DW chose not. We both survived (who had the better odds? I'm not sure, except that although we were deep into the yellow part of the CDC's map of South America, we only saw one mosquito in all of Brazil). I had some soreness and bruising at the injection site.
We both took the malaria pills. ( DW quit early). None of this cost anything significant because insurance covered almost all of it.
Of course, your experience may vary.