I had memory like this up to about the age of 16 - but I did not use mnemonics. I can't really explain it, but I was often accused of cheating in school because I could visualize a textbook page I had read and "read" it in my mind word for word and find the answers for tests. Because of this I never really felt the need to study. I was raised in a religious setting and they used this ability to have me memorize large chunks of text from the Bible - at one point I had about 50% of the new testament completely memorized.
Then one day it just suddenly left me. I'm kind of glad. My short term memory is still extremely good, and I can typically hold about 20-25 "tokens" in my head in order without issues, but converting that to a long term memory like I used to be able to do is just gone. Memory is a strange thing.
This is how it usually goes--it's vanishingly rare to retain a photographic memory into adulthood, but it's not that rare in kids. I had it too, but then I started sprouting hair in places that never ever got cold and the rest is history (that I can barely remember).
Interestingly - I also have synesthesia like the parent article's subject did, although likely not as pronounced. Not much is known about how that works, I think, I've tried to learn more over the years about it and always run into pseudoscience pretty quickly.
I remember having a similar skill when I was younger, until about the same age. When writing papers based on books, I could think about something I remember reading and know which part of the page it was on (left or right facing page and which part of the page). Then I would flip through pages quickly to find the quote.
Then one day it just suddenly left me. I'm kind of glad. My short term memory is still extremely good, and I can typically hold about 20-25 "tokens" in my head in order without issues, but converting that to a long term memory like I used to be able to do is just gone. Memory is a strange thing.