I don't know when you home schooled so I can only share what I know to be true in our area at this particular time. That said, in the past 8 years a student could be 14 and attend junior college. Last year it changed to age 16,in this particular college system. Cal State Sacramento accepted 3 of 'my'* students to take classes while in high school, based on SAT's and an interview process.
I say 'my' students because I'm an area administrator for a private school for home educated students. While I have 30 high schoolers in my campus (14 campuses in all), 10 of which are taking classes (primarily science related) at junior college. As a school we have 1,300 high school students - 550 of which are graduating high school June 1. So, my sampling is a bit larger than others.
These days there *is* opportunity for home educated students to take 'advanced' courses..via the college system. Additionally, there are a number of parents in various professional fields who give of their time..anything from tutoring higher level math, honors science, composition, art history, CLEP study groups, fitness, and more. The current homeschool community is not w/o opportunity.
Our daughter took a basic writing course at the Community College first, because on her Assessment exam, she missed the cut off by one point to get into the next level. That was fine, she needed the writing practice. After that she took the first level Engl. Comp and Lit course. She had done well enough on the assessment test to get into Pre-Calc, then Trig. Since she hadn't had high school Chem yet, she had to take a basic Chemistry course, without a lab, but after that, she took a Physics course with a lab. She was able to transfer 16 credits to the four year college she now attends. We had begun homeschooling her in 8th grade, and gave her the choice to return to school the following year, but she figured she'd just be bored, and she was right.
If you don’t mind telling me (a private mail would be fine) what’s the name of your organization? I’d like to do some research into groups like you’re talking about that “oversee” homeschoolers. Not because I plan to use one, but because it could give me some ideas about the potential for doing similar things or offering homeschooler classes.