I've also heard they've taken the word "gullible" out of the English Dictionary.
Seriously though, I think you're referring to the fontanelles which close at about the age of two. From a physiological point of view, I'm struggling to see how the closure of the fontanelles make a difference.
And remember, never ever press your finger hard into your little brothers fontanelles, even if it does make him go cross eyed and make you laugh.
