I am not felixable enough for a pistol squat as I can't get down or balance in the full dowm position, my ankles don't flex enough to get me balance right and I tip over backwards, which is probably most amusing to watch.
I can do full bodyweigh squats and sit in the asian squat with feet flat and bum on my heels/back of calfs so it is possible to be flexible enough to full sqat and not to pistol, I think this is because you are balanced in a differnt way, with legs more out to the side as you have a point of balance on each side of the body, where as with a pistol you need to get your leg more infront of you otherwise you tip over sideways.
It's not nessasarly just my ankles though, could be calfs, quads and lower back too as I understand it, I just leaned some streches to get me to touch my toes that involved loosening my back, legss and calfs, and whamo after just 2 rounds I could touch my toes when I wasn't even close before
You know all those pictures of Adam and Eve where they have belly button? Think about it..................... take as long as you need........................