1. Will removing the older Roo be traumatic for the hens (particularly the older hens that are used to him).
You do not have a 5 month old rooster. You have an immature cockerel going through puberty. This could create some turmoil if you eliminate the older rooster. It is unlikely he is mature enough to dominate all of the older hens so some of them might beat him up to keep him in line. Each chicken has its own personality and each flock has its own dynamics so I cannot guarantee you anything but I'd consider it possible it could be rough down there. He will eventually mature enough to take over and life will get peaceful when he does. Sometimes that interlude can be really peaceful, sometimes it can be pretty rough. I've had it happen both ways but I have not had any (the cockerel or the hens) be seriously injured.
2. The older Roo will be 3 years old in 3 months. Is that "old?"
I would not consider hm too old to be an efficient flock master. Each is an individual so it can vary but I'd think he probably has another two or three good years in him.
Would he still be edible?
Depends on how you cook him. Coq Au Vin is how the French turn an old rooster into a gourmet meal. Chicken and Dumplings are usually how you cook an old hen but it will work for an old rooster also. Some people would pressure cook him. The crock pot could work well.
The way I cook my old roosters is to cut them up into serving pieces. I include the back, neck, gizzard, and heart as serving pieces. I put about half in the crock pot with a bit of carrot and celery, onion and garlic. I add herbs like basil, oregano, or thyme. Cover with water. I cook that on low overnight (usually around 20 hours) and strain off the liquid. I de-fat that liquid and use it as some of the best chicken broth you will ever have. Then I pick the meat and use that for tacos, chicken salad, in soup, or to make a chicken sandwich. Then do the other half of the meat.
There are lots of ways to make a really good meal out of an old rooster but if you try frying or grilling you will be greatly disappointed.
They are all housed in a 10' x 20' run most of the time.
That's not a lot of room but you can try. Sometimes they fight to the death, sometimes they can reach an accommodation on how to work together. The more room they have the better. If you try, be observant and ready to intervene if you need to.
It is when they are out that the younger Roo tries to mount a hen which then incites the older Roo to chase him off.
Perfectly normal. At some point the immature cockerel might not run away which could lead to a big fight.
Others have said that this could not only lead to injury to the hen, but could escalate eventually to an all out fight once the younger one gets older.
Could is the operative word. It does not mean that it absolutely will. It is highly unlikely a hen would be hurt in a fight between them but serious injury to one of the fighters is certainly possible.
So instead I keep them where I know it's cooler (misters, wading pools, ice in water buckets, shade, breeze access).
