Experience is a big factor, but I think there's a limit to the amount of language learning most 50 year olds can undergo, even in a decade. But luckily for us we agree young exposure to code is a good thing :)
I wonder why you think this is true? I have personally never been given any reason to believe that a 50 year old is any less able to learn a language than a 0 year old. In fact, if you took a 50 year old and dumped them alone in a foreign country and gave them one or two dedicated language teachers and left them there for many years (which is the environment in which most children learn a language), I expect they would learn the language just as well as the child, if not better.
It's well documented that the median language-learning speed/ability of younger people is greater than that of older people.
Having said that, I do think that learning programming young is a good idea, but not because it's "easier" for children. Instead, they simply have a much longer time to get used to the "logical way of thinking" (I don't know of a more concrete term for this, but hopefully you know what I mean).
I would not expect someone who started at 10 and is now 20 (10 years experience) to be a better programmer than someone who started at 20 and is now 30, or even someone who started at 50 and is now 60.