what qualifications are needed to become a prop trader when you already have experience?

I've been a retail trader for a little over 2 years, and have found consistent profitability through trading shares. My goal is to do this independently long term, and quit my engineering job. At this point, I don't feel quite comfortable doing that because I'm not currently making enough in trading to replace my engineering salary, and haven't really been profitable for that long. But I feel I can bolster my skill by immersing in an environment where you can learn from experienced traders who actually do this for a living.

I realize there is a spectrum of prop shops ranging from those that offer a base salary and on the job training, to ones that make you pay for expensive education and kick you out if you lose money. But at this point, I've decided I'm in this for the long haul and it's a life long skill. So I want to do anything I can to accelerate this process, and spend less time doing engineer, which tbh feels like a waste of time.

I met a guy who works at a prop trading firm who says they have very high standards for those who come in and already have experience. So i'm wondering what kind of qualities or qualifications do we need to get into these prop firms, and not only that, but also survive it? I've also listened to a podcast from a guy who said their firm only retain 12% of their traders. that's pretty close to the success rate of retail traders. Are these guys who are fresh out of college or people who already have experience, but burn out because they can't handle the pressure?