@LukeAlmighty it's the "toxic masculinity" argument.
The belief is that boys are allowed to do whatever they want because society lets them.
"Grow up" means that the men they don't like are doing the same behaviors as children and teens. Flirting, sports, aggressive behavior, you know it as "being alpha" or "Chad".
Those women that don't like it see it as being subservient to men if they tolerate that behavior.
But women like the Chad anyway, they don't go for betas. "Grow up" phrase just is a way to get social justice clout. The anti-male agenda is also a way to secure positions of power for themselves. Because women now work they're in direct competition from men.