It's not so much that I can't do the math (I can't, but that's not a material issue because I don't have to). I just literally didn't understand the concept. Sort of like base 10 was how God intended it, and there is no other possible system.
I know what you mean. When my oldest was five I bought a huge box of Popsicle sticks to teach him the concept in base 10. I made up bundles of ten with him. He struggled & couldn't get it. Meanwhile, his younger brother who was barely verbal learned it. When my three year old learned something beyond the measure of many who are older, it gave me a greater understanding about differences in innate abilities, as well as different learning styles.
My oldest son's reading abilities allowed him to learn more advanced math later in his life. (He began learning to read on his own, starting around age three.) I taught my middle son how to do long division one evening. He had skipped the year of math where it was taught to his peers. This middle son is the one that learned how to do the different bases with about 5 minutes of explanation. Despite his natural aptitude, he burnt out on math during his sophomore year of HS.
I have to do work arounds for my inability to remember the multiplication tables. LOL Trust me, math concepts use a different part of the brain.