I'm more or less in your boat. My chin grows in a bit more, though still too scraggly to amount to anything, and otherwise I'm going on two decades of having a 15yo boy's "beard". While it's annoying to have certain aesthetic options off the table, it's kind of nice to have an easy routine that doesn't even need to be daily.

Shaving cream is mostly pointless, so I don't bother getting any. Shave dry if the old electric is charged, change blades once a year. If it's not, or I'm travelling, or I am feeling like I want to be pretty, then while the whiskers are still fairly soft after showering, use a Harry's 4-blade disposable (maybe ten-fifteen shaves before changing the cartridge).

I don't use it much anymore, but I also have a safety razor, and I'd change those blades after five or six uses. I can count on one hands the number of times I've had any sort of razor burn I could feel after twenty minutes, and other than the first couple of times I used the safety, I've never had more than two nicks at a time in my life, including when I was a 15yo boy. In the end, the safety is still a lot less safe than a modern disposable, requires a more consistent angle, and is just a lot of ritual and futzing that never felt particularly satisfying for me. I'm there to scrape the scraggly garbage off my face once I start looking like a patchy hobo, not to pamper myself. If doing it "wrong" came with any sort of realistic consequences like razor burn, ingrown hairs, tons of cuts, or a 5 o'clock shadow at 2:30, then I'd probably be all-in on the hobby side, but for my face it just doesn't matter. Anyway, I have fountain pens, woodworking, and mech keyboards to scratch my gleeful luddite itch.

Whenever I remember, so about twice a year. I don't shave often and when I do it's not my whole face.

Shaving my head, I change blades weekly, provided I remember. Any longer and I get razor burn. I should get longer out of each blade as I get older, at least.

I would say i change it between 4 to 10 shaves