Whenever I read up on query letters online, I only feel trepidation. The letters I've seen referenced to say things like, "I have an MA/PhD/highest degree EVER in writing, I've gone to a prestigious writing program, I've published in magazines," etc. etc. etc.
As for myself, I haven't even graduated high school yet, let alone grabbed a Masters in English at Harvard.
So my question is this: how much of an influence do the credentials, experience, age, etc. play as opposed to the actual writing? Is the fact that I am not even legal yet going to act detrimentally in any way for me?
None. I look at your writing.
If you've got good publication credits (not a fancy degree, not a fancy job, not a fancy name) I will read things that sound really stupid in a query letter figuring that you just can't write a good query letter.
If you have a degree from Fancypants U, and a stupid query letter, the degree isn't going to make much difference. If you studied at a small cow college near Bumblee, Arkansas, I'm more interested than if you skated into Yale cause your greatgrandpop gave them a building and your dad's president of the fundraising society.