I am also in my 30s with significant developmental setbacks, so I understand how it feels to feel behind others, as if you've wasted the years of your life on something that didn't work. The entertainment industry favors younger people, so it is easy to compare yourself to somebody in their teens or 20s who struck it rich due to luck or nepotism and think that you are inferior. The fact is that different people take different amounts of time. Art in particular takes a lot of time to develop.
My advice is to find the one thing you know for a FACT you are the best at, and build everything else around that singular thing. It could be something multiple people in your life have genuinely enjoyed, or something that brings you intense joy to express. Make that priority number one. Everything surrounding it does not need to be perfect, it just needs to service your core idea or talent. For example, I am great at music and writing but terrible at art, so I am aiming to create games and stories that emphasize my strengths and supplementing my weaknesses with help.
Try to identify the aspects of art/literature that you struggle with the most and see what you can do to improve them. Networking is very hard, so don't be afraid to hire or commission people if you need help. Doing things all by yourself is foolish in the age of the Internet.
I hope that helps. It is easy to think about the negatives when you reflect on a life spent in the arts, but don't forget to remember the positive experiences and the things you've taught yourself, because those matter too.
phenorax
Wish i could have something to say man but, either switch up the way you do things or go for something else.