First question, do you think you're mature enough, and are wise enough to be able to endure such punishment? Frankly said, when I first started work when I was 20 (i graduated with acca at 20), I really had a huge culture shock migrating from a full time study environment to a working one. Presently, I think all the big 4s demand much out of their staff (in terms of commitment and willingness to learn), and after what I've been through, and what my juniors have since been through, I don't think many are able to take such pressure. I've seen many
break down, cry, quit, and all end up bitter and disillusioned.
Now, I'm not discouraging you, and I think if you can take the pressure, and is willing to sacrifice a few years (you may easily wave it off as 'JUST' a few years, but it's not), I definitely encourage coming out at 20. You mature faster, and if you screw up, you have more time to recover.
But when you come in at 20, please do start with the right mindset. (many of us come in not suitably mature, which I am guilty of) Work on your appearance (it matters, alot!), try to be pleasant to have around (and smile/laugh alot!) and be tactful.
Also, be prepared to feel stupid and like there's a whole world to learn in the first 6 months. (but try to figure it out on your own). As a fellow PwC-er (and i'm sure any other big4), I do not think highly of people who needs to be spoon-fed and can't figure things out on their own even after a little guidance.
Out of curiosity, do you mean guys as well? Either way, you are hanging on really well there. I have a rough idea of who you are, since a friend of mine is from your batch..