some can lay as early as 6 months

I have read that they begin to lay:

at 20 weeks
between 4 and 6 moths
at 26 weeks

Last year I got my first egg at 17 weeks, I believe from a leghorn.

Some breeds mature more slowly than others.  EE's may take a year.  Henderson's breed chart ranks them for maturity, though some feel this chart is not all that accurate.

average ages for non-production breeds are 20-26 weeks.  production breeds average a bit earlier.  But, individual birds can start earlier.  The earliest account I have heard is 15.5 weeks from an EE.

Someone just posted that they got one at 15 weeks, 3 days... Well, I guess that's 15.5 weeks

http://www.backyardchickens.com/forum/viewtopic.php?id=193098&p=2

Don't worry they will lay and it's hard to wait lol, my 3 Rhode Islands Reds are about 22 weeks old and not laid yet but am looking forward to it very much!

My EE's are all getting ready to lay, with a few of them already started.  They are 19 weeks today, and the first one laid on my daughter's birthday (May 25th) at 17.5 weeks. 

I'm getting up to 3 eggs a day now, with more looking close!!

my barred rock laid her first egg at 5 months. my black copper laid her first today she is 6 months. my EE didn't start laying till they were a year old. watch for the squat if they are doing the squat then they are getting ready to lay.

 hi i have 2 polish chickens and they are both about 9 months of age and i was wondering what is happening