A girl found at 13 with no language tested whether it was too late to learn one

When 'Genie' was discovered in 1970 after 13 years of near-total isolation, linguist Susan Curtiss and a UCLA team tried teaching her language from scratch. She built a large vocabulary but never mastered grammar, becoming the clearest real-world test case for Eric Lenneberg's critical period hypothesis: that full grammar can only be learned within a fixed developmental window.

— Susan Curtiss, Genie: A Psycholinguistic Study of a Modern-Day "Wild Child" — Academic Press, 1977
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