if you can open yourself to the possibility of matriculating at other programs, I would apply more broadly. You seem to have a great profile, and if you can channel what you've written in your post into a coherent and thoughtful SOP, you are a shoo-in somewhere. As you already know, the programs you're applying to are, by the numbers, some most competitive in the country. Those programs receive hundreds of applications and accept ~10-20% of applicants, many of whom are admits from their undergradute program; however, if you aren't willing to compromise and are hellbent on an elite education, then don't.
Let's go concern-by-concern:
I'm concerned I didn't apply to enough schools/should apply to more. See above.
Maybe I should be aiming a little lower. See above. It never hurts to have safety schools.
I'm in my early 30s. I mean, it's fine but I'm a little scared about being in a cohort with fresh-faced undergraduates and not measuring up. Cohorts are creeping up in age. Think of what you were like at 21. You are every bit as worthy.
My GRE could be better. The first time I took it, I did worse on the multiple choice and better on the AW, so it could definitely be worse. Admittedly I'm a lot better with quantitative reasoning when I'm not a total ball of anxiety, which is why I haven't forked out another $200ish in an effort to earn back that 5.5 and push my quant up. Maybe if I fail this round again I'll revisit that. *shivers* It's solid enough that it shouldn't barr you from admission.
My SOP was SO HARD to write. As you may have noticed, I'm not very good at being brief. I'm concerned I didn't say everything I should have, or what I said may not have illustrated what I wanted it to. If there's still time, there are a handful of folk here who are willing to revise SOPs, myself included. Send me a PM if you're interested!
My old GPA is still haunting me like Moaning Myrtle and looking at it in CSDCAS was like that part in "What Not to Wear" when you look in the 360 mirror, but not getting a $5,000 shopping spree afterward. ;_______; It's not a big deal; admissions committees don't harp on decisions made a decade ago.
The idea of getting rejected from everywhere again after all of the work and sacrifice makes me more than a little sick to my stomach. Limbo is a mediocre game at best, but it's absolute murder when it becomes what your life looks like for too long. Stay strong, admissions season is mentally exhausting. Make sure to take care of yourself.