Lily & Petunia, who's older?

[hp_lexicon]

No: HPFGUIDX 41953

It is almost certain that Petunia is older, probably by at least 
eight to ten years. Lily and James were about twenty when they had 
Harry. We know this because JKR stated that Snape was 35 or 36 and 
that was after GF was published. That places the birth years for 
James, Lily, etc. at about 1960 (based on Nearly Headless Nick's 
cake for the date). 

That means that when "our story begins" in PS/SS1, Lily is about 21. 
Her sister is then married to the director of Grunnings. This isn't 
the kind of postition that a person has when they're younger than 
21. He doesn't act like a young upstart, he acts like a cranky 
middle aged member of the middle or even upper management. Granted, 
Vernon may be some years older than Petunia, but it seems unlikely 
that he's more than ten years older, which he would probably have to 
be to be a director. Sure, one can devise theories that make Petunia 
younger, but it isn't really very logical. Her behavior nicely fits 
the jealous older sister syndrome, too. 

Is this for sure? No. But it's highly probable, given all the facts 
we do know.

Steve Vander Ark
The Harry Potter Lexicon
http://www.i2k.com/~svderark/lexicon