As someone that goes through pretty much the exact same thing the only thing I can honestly say right now is to suck it up and work through it. Probably not the most helpful advice but I didn't start drawing seriously until I was in my mid 20s and I wanted to get good to supplement my graphic design work so I put a lot of pressure on myself and that was extremely detrimental to my learning process as I was demanding too much out of myself.
Don't compare yourself to others and think you should be as good as they are, instead use that to motivate yourself and work harder. I'm finally starting to get at a decent level and drawing is finally getting fun for me and for the first time I actually feel like I have what it takes to go for the long haul, but that didn't come without a lot of frustration and anger. For me the self-deprecating attitude is just a part of me and it was nearly impossible to let go but I wanted to improve bad enough to where I just managed to grind through it somehow. From my personal experience training gets easier as you go because the better you get the more motivated you get to start pumping out more work and studies, the very beginning was very tough for me because I couldn't put out a decent drawing for a long time and as a result it was tough to stay motivated. Everyone will tell you to just stop being so hard on yourself and accept where you're at and while that's the best advice you can get, if you're like me that may be extremely difficult and at that point it'll just boil down to how badly you want it.
I don't mean to deter you or anything so take everything I say with a grain of salt. This just happens to be my personal experience and everyone's gonna be different, I just figured I'd let you know what I went through as a beginner as I have a very similar personality and I'm just now starting to learn how to deal with it.