What did Vernon know about the WW?

[ratalman]

No: HPFGUIDX 67887

In re-reading SS, in the scene where Hagrid delivers the 
acceptance letter from Hogwarts to Harry, I was struck by 
something Vernon Dursley shouts to Hagrid.  Hagrid has just 
stated that when Harry attends Hogwarts, "he'll be under the 
greatest headmaster Hogwarts ever had, Albus Dumbled--"
To which Vernon shouts:  "I AM NOT PAYING FOR SOME 
CRACKPOT OLD FOOL TO TEACH HIM MAGIC TRICKS!"  If 
Vernon is not already familiar with Albus Dumbledore, how does 
he know that he is "old"?  To me, this begs the question, what 
more does Vernon know about the wizarding world?  Could the 
fact that he does have some knowledge, help to explain his great 
fear?