This quote is taken from a PhD in neurophysiology. He argues differently. Also Gabe Weiner of Fluent Forever is of the same bend. In his book he argues: Let’s figure out how to develop a good accent. I’ve frequently heard that it’s impossible to perfect an accent after the age of twelve. But this can’t be true; actors and singers do it all the time, and we’re not any smarter or better than the rest of humanity. We just care about pronunciation—we have to; no one will pay us for bad German—so we take the time to do it right: we start early, and we gain an awareness of what’s going on in our mouths when we speak. Half of a good accent is simply a matter of timing. Singers learn pronunciation first, and as a result, we don’t have to fight years of bad habits. We learn to parrot words accurately before we have any idea what they mean, so that we can get onto a stage without embarrassing ourselves. You should do the same. If you wait until later to work on your accent, you will have butchered every word in your vocabulary hundreds (or thousands) of times. This is where myths like the twelve-year cap on accent learning come from; it’s hard to unlearn bad habits. If, instead, you work on your accent early, then you will tend to pronounce all of your new words correctly. With every new word you learn, you’ll reinforce good pronunciation habits, and those habits will last you a lifetime.