Why are some people in their 30's and 40's still acting immature in their relationships or asking silly questions?

Not so long ago, I read about a man in his 30's doing a break-up prank on his girlfriend. Or a woman close to my age (I'm 37 years old) asking if her boyfriend is cheating if he's on dating sites and lying about being single. Either that or people that are still acting jealousy and throwing the ''But you said you love me'' tantrums at that age; as if they were still in HS or in their early 20's. Lastly I've read was another woman older than me by a year that was living with a lazy boyfriend that plays video games (the man was already in his 40's) and complaining that he doesn't help out, what should she do.

Seriously, what's up with those people? I think at certain age, you're already too old to be acting immature or not recognize obvious signs.

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For instance I would be too old to be talking about my latest crush. That's something a young teen would say.
Why are some people in their 30's and 40's still acting immature in their relationships or asking silly questions?
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