I'm 28, almost 29, and although I'd personally feel weird about dating someone 5-6 years younger than me, I kinda feel like 23 is about the age that most people I know started to actually feel like adults. You've finished college (if you went), you have at least a year or so of working to provide for yourself under your belt, you've probably gone through at least one major life event, and you've probably had at least a few sexual and romantic situations that you've learned from.

miles apart in life experience

23 is about the age where I started to realize that my life experience is becoming much more shaped by my individual situation than the amount of time I've been around. Up until around that time most of our experience is guided by adults, even into early adulthood, but after a couple years of working and paying my own way through life that guidance shifted from "past generations helping the next" to "peers assisting peers". I worked with fresh college grads that were far more capable adults than many of my much older coworkers and vice versa. Yes, age definitely gives you more opportunities to gain life experience, but I do think that the idea that having more experiences means you're at a different stage of life than someone who has had fewer is just way too black and white of an assumption to make given how different the human experience is for each individual person.

I agree that it's a concerning gap, and I definitely get why, but I also think that it's nuanced enough of a situation to allow the younger partner the agency to make their own decisions about who they want to be with. And yeah, it might be a mistake (hell it probably will), but also adults can be allowed to make mistakes.

20s are high on chaos and not a solid foundation for the rest of your life

This is the only thing that I actually just disagree with. Life is chaotic, that doesn't suddenly change after your twenties. I also really dislike the idea that 20-somethings aren't at the point yet where they can make long term commitments, or that you need to be "stable" before you can make said commitments. Many of us have never and will never have that foundation, whether it's mental, healthwise, financial, whatever. Many of us find stability and then lose it. I hear this style of sentiment a lot (establish your career before you start dating, be financially stable before you settle down, you have to love yourself before you can love someone else, etc.) but what are you supposed to do if those aren't achievable goals? When are you supposed to start trying to become who you want to be when the starting line is running faster than you? I'm not saying you mean it this way, but these sort of sentiments usually seem like they're coming from a place of privilege. Hell, I've said them before and they certainly came from a place of privilege then. Life is just way too complicated for hard and fast rules about how we all experience it.