It would matter if the younger ones were not laying, and it might still matter if you don't have too many 4 month old chicks.
Generally age trumps youth, but for the most part, laying hens are mature, and it really does not make much difference. This has more effect with laying hens and chicks.
Hens in home territory trump newcomers.
The number in the old flock vs the number in the newcomers, if you are adding more newcomers than old flock, that helps. If you are adding less newcomers than old flock, that hurts.
Size: Bigger trumps smaller
Mrs K