User blog:Nerakil/Bella's birth year?

So I was just on Renesmee's page, and in the comments, someone said that it was impossible for Renesmee to be born in 2006, because the wedding invitation in the film reads 2011. I said that since Bella is born in 1987 and got married shortly after high school graduation, the film must have made an error, since their wedding must have been in 2005 or so, making Renesmee's birth year 2006.

But that got me wondering, where does it mention that Bella was born in 1987? Is this just an assumption made due to the year Twilight was originally written, or is there an actual source that says she was born in that year? I'm not doubting the information here, but I'd like a book/page reference, or maybe an interview with Meyer, something official that stated her birth year, since I can't find it or recall reading it anywhere. Thanks!