infancy (n.)

late 14c., "condition of babyhood," also "childhood, youth," from Anglo-French enfaunce and directly from Latin infantia "early childhood," from infantem "young child," literally "one unable to speak" (see infant). Restriction to the earliest months of life is a return to the etymological sense of the word but is a recent development in English. In old legal language it meant "condition of being a minor" and could mean any age up to 21.