> [...] there's a limit to the amount of language learning most 50 year olds can undergo, even in a decade.
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.
Hmm... maybe this is just me not being familiar with the literature, but from that link, it looks like there are very mixed results (some studies report no difference based on age of acquisition, whereas others report that children learn more quickly/effectively). It does seem like the percentage weighs in your favor though, so I suppose I should adjust my beliefs on the matter.
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.