Although most folks who bind probably already know these things, I know sometimes it helps to actually hear from someone who has experience, so I just want to remind y'all that double binding and using a smaller binder don't make your chest flatter and they're not worth the risks.
I'm someone with a large chest. People regularly assume I'm not binding until they see me without a binder - because if you have a large chest, there's only so much you can flatten without top surgery. Unfortunately for a lot of us it's impossible to look flat even with a great quality binder and clever layering because your chest doesn't magically disappear, it still has to go somewhere.
The amount of dysphoria this caused me led to experimentation with double binding. Double binding made my chest slightly flatter - but the effect was so little, nobody noticed besides me, and the agonizing pain it resulted in wasn't even worth it. It makes it difficult to breath from basic movement, and even if you aren't moving, just sitting there with two binders on becomes painful and irritating after a few hours. Again, your binder will never be able to get rid of your chest. It can compress it, and you will find that some binders work better than others, but your chest is still there underneath your binder, and your binder can only flatten so much. If you feel as though your binder isn't binding as much as it could, look into either going a size up or trying a binder from another company.
I think the misconception that a smaller binder would result in a flatter chest comes from the idea that a tighter binder does a better job. But it actually does a noticeablely worse job. For months I wore a binder too small for me, daily. There wasn't enough room, and my chest sort of "spilled over" under my arms/the sides of the binder. On top of that, I began to experience reoccurring flares of pain in several areas even when I wasn't binding. This was remedied when I sized up, and the compression was a lot more even, therefore doing a better job.
Anyway I hope this information is useful to folks. I know it's really tempting to ignore safety tips, especially when your dysphoria is debilitating, but from personal experience it isn't worth it. And if you feel like your binder isn't compressing as much as it should, please consider buying a size or two up, or looking into binders from other companies or other styles.
The narrative that a "real" trans person would have shown "signs" of being trans at a young age really needs to die. How do you even measure that? A lot of kids didn't have the opportunity to experiment outside of assigned gender roles, sometimes because they didn't know it was a possibility, sometimes because they weren't allowed to. Even if a child expressed discomfort in their assigned gender, a parent or other adult may have forced them to suppress it, or may deny that it ever happened at all. A good number of trans people also lean heavily into gender stereotypes and gender norms prior to coming out in attempt to suppress it themselves, even if no one in their life has forced them to do so. Also...people change. Gender can be fluid. Maybe as a kid you felt content with your assigned gender at birth, but grew uncomfortable with it as you grew older. There is no way to measure or prove that someone is trans.
Guilty Gear really went and took their queer Grim Reaper character, Testament, who had been absent from the franchise for a full decade and brought them back as a canonical Transfem Enby with the character saying in their reveal trailer how much happier they are as themself now, and I am fucking living for it.