MBA at an older age for career change

I just found this site and am wondering if you have any advice. About me:

37 years old
BS and MS in biological sciences, GPAs 3.5 and 3.9, respectively.
Most work experience in clinical and biomedical research in universities/government
Currently work for federal govt, salary $90k

Basically, I am ending my third year as a federal employee and I really don't like it. My job is boring and the people I work with are either lazy or nasty or both. I've always been interested in business, but wanted to chase cures for diseases right after college instead.

Now, I'm a little older wiser and am contemplating getting an MBA to work in management/administration at a biotech or pharmaceutical company or hospital system. Or maybe I'd start a company with some science friends.

I wouldn't think twice about an MBA except for the fact that I am about 10 years older than a typical full time MBA student and that I already have $140,000 in student loans from my previous degrees. I look, feel and act young, so I wouldn't have a problem with being around 20 somethings, but the financial aspect is where I am having some doubt about if I should go back to school.

A few questions:
How difficult is it to get scholarship MBA money?
Will my age play a factor in admissions? Any programs that might be more accepting of older students?
Since I want to switch career fields, would a full time program be better than part time?
Any advice on how to do a financial cost / benefit analysis? I know a lot of the top programs have average starting salaries around $150,000. How much does investment banking and other high paying fields skew that up? Would the fields I am looking into pay enough to make money on the investment in school.
Anything that I should look into to help make my decision to go back to school?

Thanks!