For some kids, the academic part is easy; it's more often the social/emotional readiness that trips them up. The attention span may not be there for a 10-12 yr-old to sit through a long lecture. They may get restless and fidgety. They may lack the ability to listen to what others may say and participate in required group discussions. They may have limited note-taking and study skills.
The asynchronous development can really hinder kids between 10-16 yrs old. Some just don't have the motor, attention, etc. skills needed.
IF you've got a 10-12-yr-old, let's say, who are doing MOOCs or perhaps whip through a college textbook, then you've got a child who can probably do the academic work at a cc/state college or equivalent. I say probably because MOOCs are shorter in length than standard than semester length courses. Some MOOCs are more rigorous than others. And many MOOCs do not have writing requirements or other types of assessments which are used in higher ed. A lot depends on the course, instructor, expectations for the course, what will be covered and perhaps how the child handles frustration and disappointment.
Bear in mind - many schools will not touch kids until 14-16 yrs old or at least 12 yrs old regardless, due to the age and maturity. Some 14-year-old boys are pretty clueless, socially/emotionally. They can still act like 'little boys' and do rather silly things. That's the reality with some NT boys and that's the perception many in academia will have regardless of whether you have a 11-14+ age boy who could handle the academic work.
MIT accepted Ahaan Rungta at 15 yrs, but he had taken a whopping 55 MITx and OCW courses! For the article, see link:
http://news.mit.edu/2015/ahaan-rungta-mit-opencourseware-mitx-1116. Rungta was taking MITx and OCW courses at 9 yrs old but he didn't take Linear Algebra until he was ready. He was however doing university-level work at 5 yrs old and I don't think there was ever a question that he wasn't capable of doing the academic work. The question had to be on whether he could handle the social/emotional part of being physically at MIT at such a young age.
So in other words, Rungta was more than capable of doing the academic work at MIT at an early age, but he still wasn't socially/emotionally ready to physically sit at lectures at MIT campus as a full-time student until he was older at age 15 (remember, he might have been closer to 16 yrs old too). My guess is that he probably did attend lectures at MIT which were open to the public and other university-level lectures in the area.
Besides doing MOOCs and textbooks, I'd say attending university-level lectures open to the public can be a good way to assess whether a child/teen is ready for college. With higher education, a child/teen would need to be much more self-motivated, self-directed, self-initiating with their learning too.
