I don't post often, (wish I could find the time), so I'm going to remind this thread that I have 4 kids, with the oldest two having finished over two years of college credits by the time they graduated high school.
17 yo will finish with 75 credits this May. I don't recall how many my 19 yo earned, but she also earned an AA (which is 60 credits) and had some extra.
My 15 yo is currently taking several at the state college and 2 AP courses, and is hopefully going full-time in the fall.

So...I hope my insight is helpful.

Someone stated that there is a FEDERAL law prohibiting anyone under 16yo from attending universities or college...Not true at all. All three of my kids, in two different states, have attended classes on campus. I never attended a single course of theirs. My two oldest started at 14yo.
I would not send just any 14 yo onto a college campus though. I do have very specific suggestions trying to figure out if this is an option or not. I'm not going to get into that though right now, since my time is so limited.

As far as AB vs. IB vs. college courses (on campus or distance education telecourse at high school)vs. concurrent enrollment vs. CLEP- We have done them all.

AB and IB are very different from course to course, teacher to teacher. If you can, find out how many students scored the highest possible scores (ap=5/IB=7) from each teacher. My kids just asked their teachers, and they were honest. This is important to know for several reasons:
1) Are they going to have to put in extra time and work outside of class to get a 5 on AP or 7 on IB? If so, where and from whom? At what expense? Will the teacher cover all of the material to get a 5 or 7?
What we learned is that from school to school the quality of these courses varies widely. At one school my oldest attended, almost everyone scored 5s in Calc BC. At the school my son is at (a different one) only a few score 5s on Calc BC. The teachers know how many get 5s/7s. In fact, often they compete to have the most 5s/7s in a given course.
2) This was mentioned above...but for AP tests, you don't need to have taken the course. My oldest placed out of MacroEcon and English Lit and Engl Composition without taking the courses.
3) Colleges vary...all colleges. The junior college my two oldest went to was much, much more rigorous than the state college that my 2nd and 3rd are now attending. In fact, my oldest had a math teacher from MIT who had moved to be close to his grandchildren. You have to go to the university that you want your child to attend (we have a private university they all hope to go to) and ask them which classes from your jc or state college are ARTICULATED with their curriculum. (Articulate means "meets the required courses and REPLACES them." Giving credit for them means "Yeah, we'll take it, but they are not going toward your degree. They will be electives.")
For us, the jcollege that my 2 oldest went to, had every single course articulated. However, the state university only had a few. Exactly what my oldest two had interpreted as far as quality of their education.
3) Distance Education - this is when a course is tele-casted into a high school classroom. It is taught by a university professor who is teaching a real college class with students. He/She can hear the students off-campus. This is a good arrangement in that they are taking college courses with a college teacher with fellow college students. Meaning, no high school issues are involved - giving allowances where a normal professor wouldn't.
4) Concurrent enrollment - Professor or a "qualified" high school teacher comes to high school and teaches high school students. We don't do these in that it basically has no advantage other than credits earned. Usually they don't learn as much and they are given "allowances" for being in high school (such as turning in a paper late due to a competition....Not helpful in the long run.)
5)Forgot to mention this, but AP tests are not all multiple choice...English lit and composition = one example.
6) Generally, we do NOT recommend AP/IB for major courses like math and science, unless there are no other options. English, psychology, history are exceptions.
My oldest was able to take some AP/IB classes, but took many more tests than classes and earned credits. She also placed out with CLEP. She pointed out that she didn't think that through her college experience (taken in high school) that the courses/tests were adequate preparation for college. After earning AP/IB/CLEP credit,she took introductory courses for classes she already earned credit in. Many of her friends did this too. Hard to explain, but I'll try....so a 5 on the AP may get you out of a couple College Calc classes, lets say. But the university covers other information in those beginning classes. When you take Calc III, then you are confused from insertions and omissions the math dept has for their Calculus. Hard to explain, but I hope you understand.
Another reason is that AP/IB take an entire year, and each test costs money...it adds up! Jcollege/univer course is half the time usually and sometimes cheaper than the AP/IB/CLEP tests.
7) My kids now only want to take university classes. My 15yo son, many have read about before, is trying to skip the state colleges and go right to the private university...that way he is properly prepared and not wasting time. What we have learned is that state universities have easy general education classes, but not so for the upper division classes. Check ratemyprofessor.com for hard good teachers to take that know how to teach...and aren't just an easy grade.
8) A motivation for plain earning of credits is scholarships. An AA before high school graduation often earns scholarships, at least from the university it is earned from or feeds into.

Sorry it's long. I could go on. I'll try to log in for clarification if I can...if you can make sense of any of the above!