It garnered acclaim from music critics, who called the song one of the standout tracks on Paramore, and praised its production and lyricism.
Popdust gave the song a 4.5/5, commenting "The flourish of strings ... that accompanies her begging someone to admit they don't care is the power pop equivalent of a finger in the face, a thrilling moment on a record full of high points.
"[3] MTV Buzzworthy says "Here, the band swerves into new territory: synthesizers float, electronic fuzz blasts and flutters, and a mid-tempo guitar riff sounds almost ready for the dance floor.
"[4] The Stylus regards the song as "super fun and playful", adding "It’s hard not to move your shoulders to the beat and sing along".
[5] Digital Spy says "Williams's ruthlessness is highlighted best on "Grow Up" as she tells her squeeze - or more likely the Farro brothers - that she had to move on"[6] Ed Masley at The Arizona Republic ranked it as the 15th best Paramore song, stating ""Grow Up" is one of several highlights of their new self-titled album that "wears its love of New Wave culture like an extreme asymmetrical bob.