DD started racking up high school GPA as a sixth grader, too (again, with algebra I), and she was only... um... {counting} nine years old (?) at the time.
As of last spring, she was a solid 2nd in her graduating class, so it hasn't hurt HER, either.
I'd also be more concerned about what this does to the elective than about what it does to high school credits, GPA, or maturity with concepts.
My son started high school this year with several credits-- counted toward GPA and graduation-- already. The biggest con I've found is a really small one: the guidance department had palpitations trying to do his schedule this year, and we had to pull him out of a magnet track we were ambivalent about anyway to make his classes fit. For example, he's in freshman honors track in one subject area, sophomore-to-junior level in another, and in another class is in with honors-track seniors. Throw in a must-schedule extracurricular and we had the freshman office in knots.
This, though. Yes. It makes tracking/planning quite peculiar. Expect to be "that parent" in this instance. Of course, that may be more or less unavoidable to begin with with a PG kiddo.
Like eldertree, though, my DD did all of this via a virtual school. So her classmates begin the year NOT knowing how young she is, and don't necessarily ever have a reason to learn, unless she chooses to tell them. Which over time, most of them know because she has a core group of classmates that have been together for many years now...
but it doesn't matter because they all know that she's got the goods and is just the same as the rest of them. KWIM?
