Hi, like newatit2010 said, your better off sexing it first. i think you can cut the growing tip off a plant at anytime but it is best done only three time's, never do it to the end of the vegging stage, also when your clone gets to the point your able to do all this, make your cuttings in the morning instead of the afternoon or evening coz it give's the plant the rest of the day to recover.
After cutting the growing tip get it into rooting gel and the same as what you've done to the clone you got now and im sure that will grow aswell.
Anyway i hope this will help with your grow and point you in the right way.