not mature, ripe, developed, perfected, etc.
emotionally undeveloped; juvenile; childish.
suitable or designed for young people
young, youthful, or immature
"Gonna go take your sippy cup bath? Make sure to bring your baby shampoo"
"I have to go talk to him during his sippy cup cry-fest cause his girl made fun of him."
"Yeah, like that is so sippy cup already."
"What was it with rappers all wearing pacifiers and baggy toddler clothes a few years ago?"
"Yeah! Like was that sippy cup, or what?"