I tend to be an extremely cynical person because it's better to be pleasantly surprised than disappointed in people, and two, as I have stated before, I am young and immature.
Cynicism can come with perceptiveness and insight. You're young, and you see a lot to question, and perhaps rightly so. I'd always rather work with a cynic than a blind optimist, unless that optimist was loaded with cash and sharing it every few minutes.
You're likely terrified you've spent ages on your work, wasted your time, and created a monument of self-deception that will serve only to prove that your real livelihood and avocation will have nothing to do with writing.
You need to face the reality that your fears may be warranted. You may be rejected time and again, and even laughed at and mocked. Fear is crippling. Just get the manuscript in the right hands and find out if you were really meant to be a professional welder or a heart surgeon. You have your whole life ahead of yourself, and you've started it in a fine, creative way. So, go for it.
The chances any of us will become a great or successful writer are slim and dim. The advantage some of us have is that we have other careers, lives and livelihoods. If back in the day I were 18 and convinced I had to be a writer, what an awful world I fear it would have been. Writing is art, a form of expression and thought. The appreciation and admiration of others come sparingly at best.
About agents, yes, many of us can agree on a few obvious attributes that some appear to have. There are plenty of unaccomplished, untalented agents set up by some friend or family, or sitting in some institution of learning, to read manuscripts and fire off wasteful, unhelpful rejections, or who look only for a given species, and you'll find them all over Twitter and Facebook, so if you're wasting time reading posts and tweets from subpar agents, you'll only make yourself even more cynical. You're not them, and good for it, but there are also great agents out there.
I'll just repeat. You've got your whole life ahead of yourself, and your future may or may not be in writing, and you need to face the facts up front. So, confront your fears, get the manuscript out, and head off into the future that's yours.