looks like we missed the best lustrum

For Pamela and Aura, with sympathy.

It is a surprising fact that a child, during the first five years of his life, is able to learn a language -- a foreign language; for to the new-born babe all languages are foreign. At no other lustrum of his life is his mental equipment so inadequate to the task. Never is his intellect so weak, never are his reasoning powers so lame. And yet during those impotent years he can do with ease what later on he can only do with difficulty: he can master the essentials of a new language.

-- Philip Boswood Ballard, Teaching and Testing English 11 (1939).