http://fora.tv/2009/03/20/Daniel_Everett_Endangered_Language...
In this interview, Everett mentions that he met a 13 year old girl in Brazil who happened in fact to be a Pirahãn—working as a cashier clerk, fully well able to count and do maths.
I can only guess, but I wonder if yours was downvoted for making claims that seem wrong without backing them up - I don't think there is an age when new connections are no longer made nor do I agree that adults can only learn from what they already know - but I wouldn't vote it down because of my disagreement.
Though there has been recent discussion on people voting down purely for disagreement, and that might well violate etiquette. But just <0 without a comment doesn't necessarily do so.
This is why e.g. bilingual kids learn new languages much faster than people who only speak one language, people who learn an instrument as a child can pick up new ones much faster, etc.
What is a personal theory of mine is that if you don't have language to understand a concept by a certain point you can never truly understand it. The only places I point to that support my theory are the few cases of children being raised away from humans [1] and this Pirahã story. It's pretty difficult to prove scientifically since it would require destroying someone's life.
But on this site, of all sites, I would expect discussion about it, not a simple down vote.
[1] I've heard of at least 2 seperate cases where through some odd circumstanced a child reached teenage years without learning any kind of communication with humans. After they were rescued, in both cases they were never able to grasp concepts much further than a young child (around where chimps who learn sign language get to). This is by no means conclusive, since they obviously went through an incredibly traumatic experience, but as I mentioned above, there is no easy way to apply scientific method to this theory.