not a kid anymore
No longer having or afforded the innocence, naïveté, physical advantages, or lack of responsibilities associated with youth. You shouldn't try to tackle such demanding hikes—you're not a kid anymore. I could tell he was trying to con me like he used to do, but I wasn't a kid anymore, so I told him where to shove it. You aren't a kid anymore, Tom. It's time you started acting like an adult.
not a kid anymore
Fig. no longer in one's youth. You can't keep partying all weekend, every weekend. You're not a kid anymore. Kathy: Bill is just as wild as ever, I hear. Jane: Bill needs to realize that he's not a kid anymore.