I started reading comics a few months ago (I'm 25). With Batman, I started with Year One, The Man Who Laughs, The Long Halloween & Dark Victory, Robin Year One and just finished The Killing Joke.

How the heck does Barbara Gordon Bruce Wayne is Batman? It wasn't on any of the comics I've read.

Second, hwo come in Year One Bruce Wayne is 25 years old and in the Killing Joke, Barbara looks like 30 and Batman... well... 30 as well, or even younger. Is this considered canon or what?

@bornlivedie: Barbara was Batgirl before she was shot and became Oracle.

Secondly Year One isn't really canon but alot of fans consider it to be. It's actually only canon to Earth-31 which is the canon of the Dark Knight Returns and All Star Batman and Robin.

Forgot about Year One... sorry.

So, If I wanted to read about the origins of Batgirl, where could I start?

I feel like I'm missing 80% of the story reading the essentials and nothing else. It was so much more easier with Spider-Man...

Here's a list of Batman books in chronological order but take my advise, don't worry about chronology just read the good ones. If you have any doubts then you can find it on the internet or ask here.