The best way to learn proper English is to read news report, and watch news on TV. Watching TV shows is a great way to learn casual English, slang words, understand culture reference and humor. If you have already watched these shows then you may recall the words used in the following dialogs.

I'm a GROWN man
capable of living my life as I see fit.
The Big Bang Theory Season 1, Episode 4

You're a GROWN man, act like it.
The Big Bang Theory Season 11, Episode 11

And you, a GROWN man
The Big Bang Theory Season 5, Episode 16

Have you GROWN fond of me, Stark?
Game of Thrones Season 2, Episode 1

Yeah, you're a GROWN man
who's highly educated.
The Big Bang Theory Season 10, Episode 17