My father was vaccinated in the year 1918 at the age of 6. Was this the normal age for a vaccination at that time?

Also, what were the diseases the vaccination would have protected him from? Would his vaccination have had anything to do with the Spanish Flu that was rampent around that time?
This is a genealogy question prompted by discover of a half sheet paper which reads, "This day, I vaccinated John Hennessey. W.S. Brown, MD. Dec. 22nd 1918." followed by "Examination Jan 8th 1919 Results: Positive. W.S. Brown, MD."
I would certainly appreciate any information you might be able to provide.
Sincerely,
Peter Hennessey