When is a chicken full-grown

So I have something going on in my flock. We all know they aren't great quality and that they are mutts, but I believe I have come to a conclusion that I have 3 bantam birds and I was hoping someone could tell me their opinion as to whether I may be right or wrong.

I've read conflicting information on 'easy' ways to almost-age your birds (ie when hens lay and roosters crow). Is it true that by the time a hen starts laying and a rooster starts growing, they've basically grown to their potential size wise?

Thanks so much for your time on this!

They may fill out a little after, but I think her bone growth would be pretty much finished when she started to lay.

Crowing is trickier. Depending on the breed or bird, some may begin fairly young.

So of course, not knowing birth times or breed mix, it's kind of wait and see on the roo? LOL

I don't believe he has grown since I've got him, and he tries to mount my big hens and can't do anything after he manages to get up there -- he's sure given it his best try though. He has taken over 'command' of 4 of the hens (2 big, 2 small) and the large roo has just let him have those 4. If he goes after the other hens, there's a battle to be had. He does NOT leave one of his small hens alone at all, and he breeds with her a lot and she screams the whole time. When I'm in the coop she lets me pick her up and walk around with her and croons, the whole time watching him with an evil eye.

Crowing aside, if he is keeping a flock and fighting a full grown rooster, he is mature.

Oh I totally agree, if the rooster is crowing, he is becoming mature, he may grow a little more in size, but not much, filling out yes...roosters mature in filling out til well over as year, as do hens. After the first moult, then you really know what you got in hand. I would certainly bet though, if this fellow is crowing and mating that he is not growing to grow much taller. Pretty think that is the way it goes. I have a blue cochin cockerel that has began to mate and crow within the past 2 weeks, but he is still looking rather gangly, he will mature yet for a long time, some breeds mature much more quickly than others, cochins are slower goers. You got a bantam dude I bet my bottom dollar. Have a wonderful day, CynthiaM.

Thanks guys! I might keep him around. The bantam eggs are perfect for cats and dogs.

On that thought, will it hurt a bantam hen if she's with a non-bantam roo?