Wikipedia has by far the best general info on what androgens do to a female body. It can be viewed here: http://en.wikipedia.org/wiki/Hormone_replacement_therapy_%28trans%29#HRT_female-to-male
The age at which you should start is dependent on alot of things. Where you live, what the rules are regarding treatment there, when the psychiatrist assessing you feels you're ready for it, and of course, if you're legally old enough to make your own decision OR your parents are willing to give consent (as I understand your mother seems to be). My first question to you would be are you seeing a psychiatrist qualified in gender issues who could give you approval for hormones? And also, do you have an understanding GP, or can you get access to an endocrinologist who would be willing to take on your case? Other than that, all you really need to worry about is how ready YOU feel. If you're 95%* sure this is what you want to do, I think you're ready. If there's even the slightest doubt that you shouldn't do this, don't. Wait until you feel absolutely sure.
Good luck anyway man.
* I say 95% after a discussion with a friend about this. We figured that if someone was '100%' sure, they were probably being very impatient and hadn't waited long enough to figure it out. 95% seems safe because it seems to be take into consideration the risks involved as well as the certainty that this is something you need to do. Keep in mind this is my personal opinion, I'm not meaning to push this on anyone.