I have had some that are 6+ years that have never laid an egg. It has a lot to do with diet and temperature. If you overfeed them they will produce huge clutches and it may shorten their lives.
With any egglaying chameleon (once she is old enough to lay eggs), I always keep a container of washed sandbox sand in the cage to give the female a place to dig if she needs to lay eggs. If you don't do this you may miss the sometimes subtle signs that she needs to lay eggs and it can lead to eggbinding.