We have a similar path from how we were growing up vs getting better as we got older. One benefit I saw from being an overweight, out of shape, nerdy kid growing up is that I learned not to worry about what other people think or say.
"Let it pass like water off a duck's back." became a little bit of a mantra until I truly wasn't worried about it, even as I age.
Accepting that, if people wanted to be with me they would. If they didn't, I didn't want to waste my time with them. Trying to get somebody who didn't like me to like me, ceased being anything I was concerned about. Prior to hitting this point, I'd had multi-year crushes in high school on a couple of girls who were nice and friendly but just weren't interested in me.
After having this realization, it made it a lot easier to date because you can ask people out without fear of rejection. If somebody said no, great! That saved a lot of time. Don't take it personally.
The other thing that young men definitely have to learn is the gossip pipeline. Don't participate in it, but realize it is out there. Word got around in college that I "wasn't looking for a serious relationship" and it made it a lot easier for me to date. Turned out that a lot of young women worry about overly clingy men if they go out one time and then decide not to pursue it further. There's a lot of pressure on women there. People even tried to set me up on blind dates.
Eventually, I met my wife of 20 years so far.
The act of simply going on a lot of first dates is fairly validating in and of itself. Learning all of this stuff added to my own confidence too. But the absolute first step is simply self acceptance. Control what you can control, don't worry about what you can't.
And to be clear, control what you can control means that you can control improving yourself (diet, exercise, grooming, mindset, humility, faith, education, courtesy, reliability, family relationships, etc). A lot of self acceptance advice suggests that you shouldn't be trying to get better. I'm not suggesting that at all. We can all improve and we can all be better for the people we care about. That's a big piece of showing we care.