AA:
I see by your profile that you're 28, long out of high school.
The CFAT measures APTITUDE - not qualifications. Others have outlined various routes available to you (most include finishing high school), and I won't elaborate on them.
Perhaps, however, a few words from one who has been in your position (long out of high school - looking at career options).
Although I joined the CF with only a Grade 10 education, I did (eventually) complete high school - and then went on to an undergrad degree. I did this whilst serving - and it wasn't fun. I missed a LOT of time with my kids (Daddy can't play right now - he has homework to do), and it sometimes interfered with work (which, to be honest - went fairly well, I retired a Warrant, which is nothing to sneeze at - I must have been doing
something right
)
However - if I had it all to do over again, I'd finish high school - and probably achieve an undergrad degree PRIOR to having a career and family.
I don't know your circumstances, beyond your age (as posted in your profile), so I don't know what imperatives may be motivating you. I'll say this, however, if it is possible for you to finish high school PRIOR to embarking on a military career - then I'd recommend it. Given your age, however, I can see that life may not allow you that luxury - only you know your circumstances, and only you can make that decision.
Best of luck to you.
Roy