Note the pattern here. Mostly the mothers of girls had positive experiences moving their kids forward, and mothers of boys didn't. This is my observation in meat space as well.

Sadly, I fear that little boys don't mature as quickly as girls.

My experince:

Elder Daughter (still the smartest individual I know) did not have any gifted/talented programs available in the small town we lived in. So she skipped 2nd grade. There were a few social problems later - a more assertive individual wouldn't have noticed probably, but all in all, it was a good choice. When the school tried to advance her again I resisted. That was just too much of an age diff.

Younger Daughter was a late August baby & the cutoff for letting her into school was (I think) May. She was reading at a 3rd grade level and doing division before she went to school. I fought to get her into Kindergarten "early." I won. She just started at Cornell a few weeks ago. Again, there were a few problems in High School, but I think there would have been far more if she'd been held back. She tends to need a challange.

So, my advice? Get your kid in a class that challanges her. I think she's ready.