Bullshit. Even a cursory review of the research shows profound differences in child and adult learners. This is ground so well covered that it's assumed knowledge.

Have a look at (Harvard linguist) Steven Pinker's book The Language Instinct. It gives a great overview. Or if a book on linguistics isn't your thing, then read the recent studies on critical period hypothesis for SLA, such as Mayberry and Lock, 2003.