Assuming its a veiled...I don't recoommend breeding them until they are over 1 year of age and full grown....just don't like to put egglaying demands on them until they have stopped growing their bones, etc.
As for the first clutch...it depends on where she is in her cycle when you breed her. If she is already producing eggs when you mate her then the first clutch can contain some fertile and some infertile. If she is really far along in the cycle the whole clutch may be infertile and "dumped" before the normal 30days.
Since she is sexually mature, I hope you have a suitable place for her to dig in her cage??