That's not why I skin mine instead of plucking but it is a side benefit, no pin feathers to deal with. I did not have a good way to heat the water: fire risk, really inconvenient, and the wife is just as happy to not have the skin anyway.
I find that pullets even 8 to 10 months old skin pretty easily. Around 19 to 20 weeks cockerels start to get a little harder to skin, until then they are fairly easy. The older they get the harder they are. The problem is that membrane starts to grow that attaches the skin to the body. I don't know if those are tendons, ligaments, or something else. Old hens aren't that much of a problem though you might find the need to cut a few of those membrane. Old roosters are really rough, you need a sharp knife and will be cutting a lot of membrane. They also take a lot of muscle strength from you.
The first thing I do after taking the head off is to cut the feet off, that makes the drumstick a lot easier to skin. Then I put them on their back and make a slit across the abdomen. Then I start pulling and tearing, working the skin off a wing first, then the leg on that side. The wing is rough, I just keep the first two sections and toss the tip. The first problem is a membrane that holds the first two sections sort of bent, I have to cut that to even get started. Then the area that holds the flight feathers won't come off unless I use a knife to cut under it at least until I can get a good grip. I can see why people skip the wings.
My next step is pulling it off of the leg. It takes some muscle but isn't isn't horrible. If it does get hard I cut the skin where it starts to fold back in itself like turning a sock inside out. Somehow that relieves a lot of the pressure. Next step is pulling the skin off the neck, then turn it over and repeat on the wing and leg. Then pull what is left all the way to the back and cut the vent off to remove the guts. After that it depends on how you want the carcass, whole or cut into pieces.
I've never butchered a Cornish X but at that age I'd expect them to skin really easily. Pullets are pretty easy, old hens and cockerels under 6 months old are not horrible, but I do not suggest anyone try an old rooster unless they are mentally prepared for real work.
There are two kinds of pin feathers. One is actual feathers that just haven't fully grown yet. A way to remove those is to pass them through a fire. Wad up a piece of newspaper and set that on fire. The other type is sacks of liquid under the skin. These are the ones I hate and I would not expect a plucker to remove them. The only way I know to get them out is to squeeze each individual one and rinse the bird.
If you have a light feathered bird, white or buff, they are not as bad as a dark-feathered bird. The pin feathers are still there but you can't see them as well. They won't do you any harm to leave them but the carcass is not pretty with a dark-feathered bird. I can't stand to leave the dark liquid pockets and generally remove all the small feathers too.
