Adding new, fresh blood to my small chicken flock

My chooks are coming into full maturity, laying about one big, beautiful egg per day. I bought them in two sets of six, in 2015, in January and March, more-or-less. Thus, spring 2016, they'll be a year old. I have ten. Well, actually nine hens and Big Roo.

I;m thinking about getting six more chicks in the spring, to keep the flock in rotation.

When do my chooks reach full maturity? Is my strategy to add six chicks per year a good idea to always keep my laying productivity to its' max, over the years?

I want to keep my small flock fresh with young blood.

What do you think?

Commercial egg farms rotate the old hens out after a year, but the drop in egg production is often hardly noticeable on a homestead scale till the birds are at least three years old. So you can save yourself the bother of raising new chicks for another couple of years. And if there is a rooster, you could always try to let a hen hatch her own. Some breeds are better than others at this, but if a hen goes broody....wants to sit on eggs and fusses at you if disturbed, that's a good chance that she is game to sit on eggs. Of course, half the chicks will be roosters, but if you have enough young hens, then you just eat the young roosters, along with the old hens, and then you're left with new hens. Since any rooster from this process will be related to the hens, it's best genetics-wise to bring in another rooster from somewhere else to keep the process going.

^^^^^^ chickens were raised like this over many generations across America, if you start out with several unrelated crossbreed hens and an unrelated crossbreed rooster, you would have enough genetic diversity to keep your flock going for a very long time without outside input, just raising from your own brood.