It's probably slowed their growth rate a bit due to the lower protein content. Layer feed is a bit too low in protein for a growing, developing bird and it's got a lot of extra calcium added to it. This calcium is great for hens that are laying, because they need it to produce good, strong eggshells without depleting their own bones. But that calcium is dangerous for birds that aren't laying. It can't be expelled and builds up in the kidneys. It will cause the kidneys to shut down eventually and may shorten a bird's life span by several years.
The most simple and safest way to feed a flock with different ages, and roosters is to feed a grower type feed, and supplement the layers with some sort of calcium source. Excess protein is expelled in their feces, so there is no toxic buildup in their organs. The higher protein content also helps keep them laying if you give a lot of treat items (veggies and scratch grains), and reduces egg eating and feather picking. It will also help molting birds to regrow their feathers faster.