How long till I can get into pointe shoes?

This is my 4th year of ballet. Like, since I'm doing ballet this year, in 2013 I will have accomplished 4 years of ballet. Now, I REALLY WANT TO GET INTO POINTE SHOES! But, idk when. I asked my ballet teacher, but she didnt really answer my question :/ So... maybe you can tell me how long it took u to get into them? And what are the requirements to get into them? thx a bunch!