Why are some people stuck at teenage mentality?

Last week I bumped into an former male classmate. He's older than me by 2 years and he was a jerk in HS. Apparently he's now a doctor.

The conversation started good but then he started with his bad jokes again from back then. He did the same exactly thing that got me upset back then. I called him out on it and he got defensive once again saying he was just joking and asking ''can't you just take a joke'' (the same question he asked me when we were teens)?

So a 32 year-old physician that's into childish jokes still. Wow. Why are some people still acting like teens even when you're adults already?

Why are some people stuck at teenage mentality?
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