I don't think there is a minimum age to compete in the NCAA, I'm not up on the JC rules. A prospect would need to have met the standards for the number of core courses completed in high school to be classified as a full qualifier (eligible for varsity intercollegiate competition and athletic based financial aid), which could potentially trip up someone who took an accelerated path through high school.
In my 12 years coaching I've had a number of 17 year olds run on our team. About the only difference we deal with is their parents have to sign the NCAA compliance forms.
Amobi Okoye played DI football for Louisville in 2003 when he was 16.