There will certainly be a question included on the assessment which will ask if you are at least of a certain age, which regarding the position you're not, and therefore the computer system would probably disqualify you based on that alone.
I will say however be very cautious when making these decisions, I am twenty three and have been flying since I was 18, and went to school simultaneously during points in my flying career, and it's very difficult. I recommend attending to education and then flying after or towards the end.
Don't get stuck working for any airline that has less than three FAs on board their aircraft as it will simply suck, and honestly don't believe experience is important as education. If flight school isn't your thing, and your sure of this given your already substantial investment, I would recommend finding something else completely different, applying credits towards a degree program elsewhere as this will look very well to any on-board services department in the future.
Also, there will be a lot of retirements in the flight attendant position over the years to come, so working on a second language could also help your chances of establishing a position with a major network carrier.
Think about the types of flying your drawn too, you've mentioned Southwest. However Remember about southwest, it's renown as a great company in the industry, but over the last few years WN
hasn't been proofed from the struggles the rest of the industry has either, and has in many I've talked to opinions, changed their views on a lot of labor related activities which still remain a fundamental blueprint of their success. They are certainly going through changes there with their business model however. I know their FAs are the best paid (for now), but they also fly, what some would describe as, harder schedules.
Don't get me wrong, I would have loved to fly for Southwest if I would have had the chance too before where I am at now, but these are just things for you to consider from one young guy who's spent time in this industry to another contemplating a career such as this.
And let me tell you by the way, being a flight attendant is so fun, especially if you love planes. You make a lot of friends, and build amazing memories. If you want more pointers drop me an e-mail.