1) Everywhere that I have looked, they say to avoid a "save the world" or "I'm gonna do good for people" direction because it comes off as naive. Does my PS come off that way, particularly towards the end? I try to avoid it, even going so far as explicitly stating that I won't save the world. But I'm wondering if that actually exacerbates the problem.
It does a little bit. I think it wouldn't come off that way if you were to give a specific field that you are interested in. You can't help people all over the world. Are you interested in international law? A field of law involving technology. It comes off like you can help people around the world in whatever field of law that interests you, but you can't
2) I delve into quite a few aspects of my life during the PS. Is it confusing? And if there are disconnects, where do they occur?
I did notice that you started talking about high school, then started talking about when you were 10 or 12, then bounced back up to high school again. I would go in chronological order. I don't think you need to specify age (expect for maybe when you were 12, because that was impressive
3) Does it sound mature? This is perhaps my biggest concern, especially with the discussion of magic at the beginning and the ending which might come off as naive.
I think the bit in magic is a unique way to lead into your topic. You don't come off as immature or naive to me.
4) Is it interesting? It seems like, if it were someone else's personal statement and I were reading it, I would be interested. But it's my life, so of course I'm interested! Do you find it interesting?
Its interesting, but I see how it can become boring when you write for a while about what you did as a programmer. I would focus more on the role your work played on your personal development. What qualities did you develop that would make you a good fit for the practice of law.
Finally, if you are going to mention the school's name, don't do it the way that you did. It will be vary obvious that all you did was change the school's name for each application. I would either give more detailed information about how a particular school would help you in your career of law. What abilities will you acquire at school XYZ? What classes, programs, internships, clinics, etc. do they offer you that would make this a good fit for you career interest? If you keep the last few sentences as they are, I think you would be better of removing them.
I hope that helped.