Any reasons why people offensively called me a child/kid when I was an adult?

Kid and child are technical terms, not relative terms. I hated it when my stepfather called me a kid this year. A clinician said it was rape and that I was a child when I said I dated a 55-year-young lass at age 18. A contemporary pupil called me a kid at 18 as well.

Any reasons why people offensively called me a child/kid when I was an adult?
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