I'm so frustrated. My wife needs to grow up.
Can you explain why you think your wife needs to grow up?
She is always picking problems with me over nothing.
It's okay to think someone is not being mature. Be respectful though when you tell her this instead of being blunt.
Fine then I'm telling her to grow up.
Say something more neutral instead of telling her to grow up. Point out her flaws in a calm and rational manner.