I have never been able to, even as a child. I could flip straight back into a crab and all manner of other stretches, but I could never touch my toes. I still can't at 30.
I've been doing Pilates and yoga since Christmas, and though I've never been very sporty I've always tried to do some exercise so I'm not hugely unfit or out of shape, but I cannot get my fingers even to my ankles. Other people who do no exercise or stretches can do it easily. Is it something that some people just physically can't do? And if so, why? Or do I need to just keep trying?