You can knock out some of your GE classes at a community college to save money, and then finish up with ERAU's extended classes or online while at FSA. I knew several guy's when I was there who would drive up to Patrick AFB in the evenings from Vero to go to Riddle classes.
As for the amount of time to get through MEI, that is solely up to you. I know a few guy's who finished up at safety in 12-14 months (rare, but possible). It is up to you.
As for your age and the success rate of someone your age at FSA...When I audited the instrument ground before starting my CFII, there was an 18 year old in my class. He failed most of the exams the first time around. What does this mean? Was he unable to keep up because of his age? I don't think so. I don't think he was serious enough about what he was doing. He had admitted to me that he was still in the high school mode/mentality. He did wise up and go on to complete his CFI ratings. Once again, it is all up to you.
When you do go, enter the program focused and with a clear mind. You will have alot of money on the line and review flights can get costly. Most importantly, have a good time and absorb as much as you can while you are there. FSA is a great school and you will learn a lot.
As for FSA gauranteeing you a job, I don't know where someone got that idea. If you focus and work your butt off, then you should do just fine in the CFI interview.
Any questions about FSA PM me.
Good luck...ILS