Skinning is just such physical work to me, I don't love doing it. Now, the next time I want to skin one, I'm going to try hanging by the legs in order to do down over the wings so that I can actually get some purchase and leverage, so that may help. Of course, I'm sure young birds and especially broilers are probably easier to skin than the typical older roosters and hens I usually do.
Absolutely. I find that skinning a cockerel starts to get hard around 16 weeks. Different ones mature at different rates so that can vary. By the time they hit 23 weeks, my normal butcher age for dual-purpose cockerels, they start to get rough. An old rooster, well that can be a real challenge.
I tend to butcher my excess pullets around 8 months, they are not too bad to skin. Some older hens can be challenging but most of them aren't too bad. Sex and age has an effect on how hard it is.