To grow too large for something, or to mature beyond something and no longer be interested in or suited for it.
From out- + grow (Old English 'growan'). The prefix 'out-' adds the sense of exceeding or surpassing, creating the meaning of growing beyond limitations.
Kids actually outgrow clothes measurably—children grow about 2.5 inches per year until age 3, which is why toddler clothes are built with growth in mind!
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