Why do some people tell you to "grow up" when you have a differing opinion to them?

Why do some people immediately resort to telling you to "grow up" and call you childish just because they hold a different opinion to you on something? Like if you're debating and they disagree with you, and then they say "grow the fuck up." Like why? Do you find it condescending/patronising when people say this? How do you respond?

Why do some people tell you to "grow up" when you have a differing opinion to them?
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