The timeline on the DVD *confirms* canon.

[Alia]

No: HPFGUIDX 55892

--- In HPforGrownups at yahoogroups.com, "gwendolyngrace" 
<gwendolyngrace at y...> wrote:
> I definitely agree that dates and numbers are not her strong suit. 
> 
> However, what's wrong with a "school year" cutoff? 
> 
> Say that Professor McGonagall consults the rolls in early spring of 
> the current school year. Any witches or wizards who will be turning 
> 11 *at any time* between the end of the current term and the end of 
> the *next* school year get their letter that summer?
> 
> Okay, so for some Muggle-educated kids, this may mean that they 
will 
> have already started at a secondary school before they switch to 
> Hogwarts. So? I'm sure it's not unheard of for people to change 
> schools even a year after starting. Usually it's because of moving, 
> but I would think there are many times where the parents and 
teachers 
> feel a student will perform better in a different setting. So they 
> pull the child out of the school where they've just spent a year 
and 
> next term pop them in elsewhere. Or is that completely forbidden in 
> English schools? Once you start somewhere, that's it, unless your 
> family moves to a different jurisdiction?
> 
> By that logic, Ron was born in 1981, which makes him younger than 
the 
> other two, which IMO does make sense. 
> 
> So if the end of term is around June, then there'd be a roughly 
> June/July cutoff, and all the kids in a given first-year will 
> celebrate their 11th birthdays through the course of that year.
> 
> Gwendolyn Grace

Here's a thought - When I started school, if you were going to be of 
age by the end of the calendar year you could start. So if the age is 
11 for Hogwarts, then one must turn 11 by the end of December to 
start in September. I have heard of other schools having the cutoff 
as the end of September. 

If this is so, then Ron, Harry and Hermione would all have been born 
in 1980 with Ron's birthday being the earliest, and Hermione turning 
11 during the first month of school. 

Another thought - as it's for high school, it could be that 11 just 
is the average age. So, if a student had advanced faster through 
primary school, he/she would start Hogwarts whenever they would have 
been going to high school.

Personally, I think it is the first option and that all three were 
born in the same year.

Cheers,
Alia