How to introduce your chicks to the flock, and at what age can we start it

[Sawyer2010]

Hi! So we had 4 “pullets” but it turns out we had 3 hens and 1 roo. So unfortunately we had to get rid of him. So I bought a few more chicks. At what age can I start to slowly introduce them to the rest of the pullets and how do I do it.
The new chicks we just got are under a week old. And the pullets we have now are 15 weeks old. At what age can we start introducing. Just trying to plan ahead.

 

[azygous]

Female chicks are called pullets. How old are the original pullets? How old are the new ones? That's kind of important information.