I don't know how much room you have or how your room is set up. That is pretty important. If you have sufficient room it could be pretty easy. If space is tight it could be more of a challenge.
@aart has a copy and paste section that gives the generic recommendations which are as specific as we can get since we don't know what you have to work with. Hopefully she is online and willing to share.
If your six month olds are laying the older ones should treat them as adults. They will sort out the pecking order and soon merge to one flock. It's often a little more violent but is typically quickly settled. The more room the better.
If the young ones are not yet laying they will likely stay separate from the older ones, sort of forming a sub-flock. They will probably avoid the older ones during the day and not sleep on the same roosts at night. If you have enough room for them to avoid the older ones day and night it's usually more peaceful but takes longer. There are always exceptions since you are dealing with living animals but we are talking generic, not specifics. If space is tight it can become quite violent.