As stated before depending on the breed they start laying anywhere from 5 to six months, some of the larger breeds can start to lay even later.
In order for your hen to hatch eggs, she has to go broody first. Not all hens go broody. If you get a broody hen and let mother nature take it's course, you should have a pretty good success rate.
If you plan to incubate your eggs, definitely wait until you get consistent size eggs. Maybe wait about a month after they first start laying. Don't be in too much of a rush. It is so tempting to get those babies going right now, but I think, if you go along with what would be occurring naturally, you'll get sturdier chicks and have a better experience all around.
We hold off until March to get our babies started. I like to have two hens go broody at the same time, so they can share the mothering duties. That way there is less wear and tear on the momma hen.
Good luck and enjoy raising your own.