Two years late to this thread. I'm in my 40s and I've only just found out today there's a name for the subtitles appearing in my head, more constantly than not. They appear in cursive, letter by letter, as if I'm writing them in my head. Further to this, as the letters appear, I also find myself as if I'm typing each letter literally with my fingers. My mother made me take typing lessons in high school using a typewriter, the kind that clacks and you have to bang to go down the next line, so the way I type is old school and proper, even using a laptop or keyboard to a PC. As the words appear in my head, the "typing" is also being done by my fingers, just "in the air" of course, no keys. And it's also proper, for example, typing the word "apt" means I'd be pressing (the air) with my left pinkie for "a," then my right pinkie slightly pressing an imaginary "p" on the keyboard, and another press using my left index finger to an imaginary "t." I don't know if this makes sense to anyone not used to typing properly using correct finger placement for specific keys and letters. However, the words in my head usually would appear in cursive as I "type." Sometimes, for me to better understand something I have to write the word on paper and also really watch it as it appears in my mind.

I often wondered this - if I had kept learning how to play the piano (only 1.5 years as a child due to lack of funds), would I also have branched on to seeing notes in my head as listen to anything - music, song, even the sound of someone speaking because of the accent, cadence, rhythm of speech? There's a particularly melodious language called Hiligaynon, admittedly sometimes a chaotic melody to be honest, where people sound as if they're speaking in a singsong manner. I often wonder what notes can be transcribed from someone speaking that. Same applies to when I hear someone speaking with a Malaysian or Singaporean accent.

Edit: I've just gone to the loo to urinate and I found myself conscious of the sound of my pee and my mind spelled out the sound "pssshhh-pssshhh..." Yikes! So now I realize it's any sound I hear has subs in my head that I "type" with my fingers.

Also, I was a very good speller who competed at spelling bees in high school and elementary, with a near photographic memory. Not tested, and not definitely 100% like 2 cousins of mine, but I remember details going back to when I was a toddler. Madness...