i had some baby guppys about 2-3 months ago and i would like them to grow to full size so want to seperate the male and female about how long will this take before i can tell? some alredy have colour

As long as they are in a large enough tank, they will grow to full size. It will take about 6-8 months, depending on your water conditions.
Oh, and you don't have to separate the two unless you don't want anymore fry.

Guppy breeder =]

if the tanks big enough they will grow to full size anyway but feed them cucumbers and daphnia or baby brine shrimp they will grow to adults within 6 months and you dont need to seperate males and female unless you want to create your own strain.