Right. Your revision is much better. I would hyphenate "grown-up" when it is used as an adjective.
Interested in Language
I think this sentence is wrong, isn't it?
"He talked to her like she were a grown up person"
Shouldn't it be :
"He talked to her as if she were a grown up person" ?
Thanks in advance
Grown-up = adjective
Grown up = verb form
Grownup = noun
Remember - if you don't use correct capitalisation, punctuation and spacing, anything you write will be incorrect.
I hyphenate the noun too.