" As always, there are exceptions. Adults with training can still learn to distinguish speech sounds in other languages. But in general, the brain appears to have a limited window of opportunity in an astonishingly early time frame. The cognitive door begins swinging shut at 6 months old, and then, unless something pushes against it, the door closes. By 12 months, your baby’s brain has made decisions that affect her the rest of her life. "

― John Medina , Brain Rules for Baby: How to Raise a Smart and Happy Child from Zero to Five