I don't worry too much about it with feedstore/hatchery chicks. I'd quarantine if they were on the ground at another farm. There's enough of an age difference that you'll need to keep an eye on things and make sure the younger batch doesn't get picked on. It could very well be fine, but I've had it go both ways so just watch them for awhile. Good luck and enjoy those new fuzzy butts!
No need to quarantine when they are this young. Just put them all in the same brooder. Keep a close eye on them for awhile when you put the younger ones in the brooder. Keeping an eye on the for awhile is not a problem for most of us...
Please please please! Always quarantine! There is always a reason to worry with ANY new birds.
Age does have a few factors when it comes to disease and parasites however even chicks who act fine can be ill with something contagious.
Be on the safe side and quarantine them, wait at least two weeks if not more to introduce them to each other.
Age has nothing to do with quarantine. Just ask gumpsgirl, who had a week old chick pass Coryza to her flock about a year ago. They can come with disease, though generally, most folks trust chicks straight from the hatchery. The problem with feedstore chicks is that they may let folks handle them (mine does not allow that) and that can pass disease. Or the brooder could have not been disinfected properly between batches at the feedstore. You just never know. If they have just come in from the hatchery and you snatch them up, there is less chance of disease (but it's not foolproof since hatcheries are usually not always Mycoplasma free, surprisingly)