Thread: How long until i can do a complete pull up(chin up)?

at the moment i am 14, 140 lbs (yah, im a bit chubby), about 5 and a half feet tall, and i hardly have any arm muscle. A few days ago i got the iron gym pullup bar,which is really worth its money. But what i want to know is how long it will take me until i can do a complete pullup or chin up.I can really only do like a quarter of one now. Also, i would like to know how i could go about doing more pullups/chinups

Thxs