"Have you ever heard anything about God, Topsy? ... Do you know who made you?" "Nobody, as I knows on," said the child. ... "I spect I grow'd. Don't think nobody never made me." [Harriet B. Stowe, "Uncle Tom's Cabin," 1851]
Grown-up (adj.) "mature" is from 1633; the noun meaning "adult person" is from 1813. Growth is first attested 1557, on model of health, stealth, etc.