I've heard of Bard at Simon's Rock, but don't know anything specific about the school. If you're fairly sure about what you want to do, you feel prepared for college, and your high school courses are unchallenging, you might benefit from early college.
Here are some things I would worry about though,
1. There are cheaper ways for high school students to get college credit.
a. You can take AP courses for free.
b. Some high schools allow students to take courses at a local college for free or at a reduced rate.
c. You could prepare for AP courses on your own, and just arrange
to take the test.
2. Many people your age change their minds about what they want to do. If you need more time to decide a major, it might be better to stay in high school and give yourself some time to decide rather than paying for college while you decide.
3. Simon's Rock is a small school. It is probably a good small school, but it is not amongst the best in the country in any area. If you know what you want to do, would you rather go to a school that has a highly ranked program in your major? If you decided you were interested in a business, engineering, or other program not offered at Bard, you would need to transfer.
4. If you transfer from Simon's Rock to another school, the credits should transfer, but some may not fulfill certain general ed or major requirements at the new school. So, transferring may cause some minor issues.