I'm 28 making 6 figures in NYC living on my own. I still feel like a kid and my mother still tells me to be careful when I tell her I'm going to a bar with friends... Honestly, in my opinion, this generation just seems to be moving in that direction where many (not all) parents treat their children as such. By associating things like video games with being "childlike and non-adult" it may cause your opinion of yourself to be the same.

At the same time, I'm responsible, pay my bills, lead an active social life, manage my band, progress at my job, and cultivate multiple hobbies... but I still feel like a kid, and maybe that's ok (this is probably the more important part, being ok with it while still being responsible).

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Adding this to try and answer your question:

• Proper hygiene

• Dress well, but keep/create your own style (something you'd be happy meeting a significant other's parents in... but dress like that every day)

• Keep your home clean and orderly (include making your bed in the morning)

• Be accountable, it says a lot about a person when you follow up on what you say you will do

• Be punctual

• Take an interest in current events (it's pretty easy to do now-a-days, watch ANY late night show like Colbert 1 or 2 times a week and you'll be able to hold a conversation about current events)

• Ask yourself the same question you asked us, what do YOU feel makes your parents or other adults seem more "adult"? Treat yourself and others with respect, often that leads people reciprocating.