Here's a quote, FYI, from the Public Health Canada website:

In 2001, a syndrome of fever and multisystem organ failure was first described in recipients of YF vaccine and is now referred to as vaccine associated neurotropic disease (YFV-AND). All affected persons have required care in an intensive care unit, and the associated mortality rate is estimated to be between 70% and 80%. YFV-AND has previously been reported in young infants but has now also been reported in older adults. The risk of YFV-AND increases with age: the rate is estimated to be 1.1 per 100,000 doses in persons ≥ 60 years and 3.2 per 100,000 doses in those ≥ 70 years. From data collected through a passive surveillance system for adverse events following immunization in the United States, the reporting rate of any serious adverse event following YF immunization was higher among those ≥ 60 years than younger adults (4.2 per 100,000 doses compared with 0.7 per 100,000 doses, respectively). For YFV-AND specifically, the rate was 1.6 per 100,000 doses in persons ≥ 60 years.
[...]
On the basis of the recent reports of adverse events in older travellers, already discussed, immunization in those ≥ 60 years of age should be carried out only after an individual risk assessment.