Good day Nairafolks,
I noticed my female cousin though she is around 18 now she still behaves and reasons like 14 year olds.

Not like really 14 year old she's mature and all physically but her behavior ( not all behavior though) most of her behavior she can play with little children and all, each time I call her to notice that don't you know you are older than all this she would just frown at me, she can cook do all the rest and everything, her hand shakes also sometimes when she's frightened.

What could be the cause and remedy for it?

Well this is exactly what they all complained about me at home

I guess she's my twin from another family 😂😂😂
Please leave her alone

We are not just equal. Some are matured souls coming back to earth while others are young souls.

badboyTee:
■ Good day Nairafolks, I noticed my female cousin though she is around 18 now she still behaves and reasons like 14 year olds.
Not like really 14 year old she's mature and all physically but her behavior ( not all behavior though) most of her behavior she can play with little children and all, each time I call her to notice that don't you know you are older than all this she would just frown at me, she can cook do all the rest and everything, her hand shakes also sometimes when she's frightened. What could be the cause and remedy for it?

Please leave her alone and stop bothering her. Let her enjoy her childhood for as long as she can. She is not immature. She is still a child at heart and there is absolutely nothing wrong with that. Stop monitoring her and keep your sense of maturity to your own self.