I hear that deer meat, that free-roam and are wild, is tight and bitter. Cow and chicken, that do not move much, tend to be tender, and fat-rich.
I'd venture a guess and say its like deer meat, or maybe bear meat, which I tried once and was disgusting; tight, foul-y, and dry.
They only don't move much because of intensive farming practices that pack them into small places to prevent movement (partly for cost efficiency, but also because Westerners have become accustomed to this mild flavour profile).
If you let your cows and chickens range free and don't supplement their feed, they tend to be lean, heavily muscled, strongly flavoured, and often pretty damn tough.
Anyway, grass fed pasture beef is a bit leaner, does have a strong flavour, but the tender cuts are still tender. It's not close to grass fed lamb w.r.t. gaminess.
Old egg laying hens are tougher and have thicker skin, yes. Just put them in a stew.