No, it's on a percentage. Like Gimmepienow said, I think it's a 12% rate that you can get a female starter, and a 88% rate you can get a male starter. Obviously, male is much more common. Getting a female starter is like winning the lottery. There isn't much of a chance, but still possible.
XP Well, I really did 'win the lottery' with this one!-
Okay, feel free to believe this or not- but the greatest stroke of luck overcame me when I was playing leaf green a few months ago. You see, when I start a new pokemon game I like to randomly pick my starter by swirling the buttons and covering the screen. Then (because I'm weird) I try to go as long as possible without finding out what my pokemon is. So I was playing my game and I was asked to nickname my pokemon. I still had no idea what it was though. When I was beginning to nickname it I decided I would confirm it to be male, so I took just a little peek to see the gender, still not wanting to give away my pokemon. I was surprised to see a female, so instead of using my originally planned name, Lucky, I called her Shimmer. And then my rival challenged me to a battle, but now I had the volume up. So, my pokemon was revealed to be a charmander, because I'm that good with calls. But I heard a strange noise after the call and so I decided to look, and ho and behold I was met by the fearsome posture of my female
shiny charmander. Now, I'll tell you all, I have no skill at all with 'jumping off of walls', but that moment was the closest I came by far. Yeah, female
and shiny. That was some lucky game! Now I have my female black charizard so ironically named Shimmer. Maybe that is why my sister told me that I was half phione, because they are said to cause great luck! And that is the story of me being a winner, XD!
Sorry everyone, I know that was long! -_-