Harry doesn't know Re: Lifespans?

[potioncat]

No: HPFGUIDX 131649

Potioncat asked:
> >And another thought just crossed my mind; I wonder how many of the 
old Headmasters DD actually knew.

Ffred answered:
snip 
> Given that Marchbanks is that much older than Dumbledore, it's not
> impossible that Dippet was already Head when Dumbledore went to 
school in
> the 1850s, perhaps aged about 100 when he took on the job..
> 
> It's not explicit as to whether there was another Head between 
Dippet and
> Dumbledore.
> 
> I'd go for a minimum of one, but more likely two

Potioncat wonders again:
Well, as I make it out, and I'm as good with math as JKR is, Phineas 
Nigellus could have been born born around 1815. (One of many possible 
dates) That makes him only about 25 years older than Dumbledore. I 
wonder if PN was the Headmaster before Dippet? Although, he seems too 
young, doesn't he? Or could he have been between Dippet and 
Dumbledore?

You would think if he was too long ago, Sirius wouldn't know much 
about him. And for that matter, I wonder how Sirius knew PN was so 
unpopular?

Here's how I came up with a possible date. For an arbitrary reason, I 
made most of the generations 30 years. That's on the older side. I 
also made Sirius' parents older than that, given that Mrs. Black is 
an elderly witch in her portrait.
 
So: Sirius b 1960, Mr. Black 1915, grandfather 1875, Great-
grandfather 1845 (about DD's year), great-great-grandfather 1815 
(Phineas).

It makes sense that DD might have had reason to know several of the 
Headmasters either as a student or a teacher or just in the WW. How 
does that sound?

And, now it crosses my mind, those Blacks don't live very long lives, 
do they?