The question of origin is still pretty unclear. There seems to be a tension between things that are more developmental (if you have mental imagery, for example, you seem to be able to get better or worse) and those that are likely genetic (research does suggest a connection between aphantasia and autism spectrum etc).

As someone said below, I suggested figuring it out early is best because of a lot of things that just work differently, especially in learning. There seems to be a real selection bias that most people who learned they were aphantasic reading a New Yorker article, say, by definition figured out how to make it work somewhere along the line. Aphantasia isn’t at all a learning disability in a real sense, but you definitely have to approach things differently.

I think it’s because you can find supports to help you learn.

I’ve been teaching math for almost 18 years at this point, and only a couple years ago learned that I lean towards aphantasia. Back in high school, geometry was HARD. Calc 3 was HARD. It was presented as visualize and imagine, and I tried my best. It just turns out other people could do that, and the fuzzy thing thing (or, more commonly, the ‘bulleted list of information’ that make up my imagination) was not “normal.”

If I’d known this (and my teachers were in a position to also know this), then maybe we’d spend more time with external visual models (what Geogebra now does for us, for example) to help me out.

Now that I teach future high school math teachers, it’s definitely something I talk about to normalize “not everyone can see in their mind.”