I would say too young, only because I just tried to intergrate my 23 9 week olds with my year old flock and now I am nursing a welsummer pullet from getting the back of her neck pecked clean to the bones and bloody. And I have a very large coop and the old gals free range all day.
I supervised them for a week and all of the sudden I found that pullet huddled in a corner of the coop.
If you have room in your coop make a corner fenced off and wait till they are more the same size. I now play chicken shuttle, I shuttle out the year olds to the pasture, then I shuttle the 10 week old pullets out of the large brooder, through the coop and into the side fenced chicken yard, then I re open the coop so the year old hens can come in use the nesting boxes to lay thier eggs. In the evening I get to shuttle all again. Soon I will intergrate again YAY