How do I move away from the adolescent mindset?

I still think and behave like an adolescent a lot of times, even subconsciously without fully noticing. I am 21 now and am not a teenager anymore. There are guys younger than me that are more mature. There are guys my age who are married and/or have kids of their own already. How do I let go of this mindset and start viewing myself (self image) as an adult?
How do I move away from the adolescent mindset?
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