First of all, a super idea to share our mistakes in one forum.
Now life regrets or mistakes. I did not do much in my life. I'm getting to my sixties now, and I have things that I would have done differently. First of all, would be less worrying, because most of my worries never materialized. And it is the same with most of us. I was holding back a lot and wasn't doing much of what I wanted to do. I was beating the same path as everybody around me did. Maybe times were different than they are now, but I don't think so. Human nature rarely changes. You will get a lot of influence from your surroundings, good and otherwise. People will influence your decisions, so you have to make sure that people that you have every day, are similar in the way of thinking and have at least a similar worldview. Otherwise, you will be sucked in, and you will live other people's life. What I mean is you won't be living yours, because you will forget about it soon enough, and you will do what others are doing. The same happened to me. "Do you want to write? do you know that writers make about 5000$ per annum? Plumbers can make triple that." I don't say that I became a plumber, but I say that I became neither. Just because of someone's stupid remark that he forgot 10 min later. He himself said me so. And I was fighting myself by indecision. What I want to say is, if you want to be an astronaut or a pet groomer - be. Another thing that I found out only later in my life is reading. If I have read those books I have read recently, my life would be so much different. Read, and read a lot. And you will see how your worldview changes, how your thoughts change and then your life.
I learned: don't worry, there is nothing to worry about. Nearly all of my worries never materialized. Do what you want to do. If you want to write right, or if you want to be a plumber, do it. But make sure it's your own decision. Don't criticize someone's decision to be this or that, you don't know how much you can affect someone else's life. Surround yourself with people that think similarly and have a similar worldview. It is so important! Kill indecision, it's an enemy. Read books, read, read and read. It is the thing that I regret because all other things would never have happened.