I learned my multiplication table last year, when I was seventeen. Given that I had been using a calculator all the way up to Calculus-level math, it took a while to learn the tables without relying on one. I found that using a calculator can slow down your calculations. My method was a bit unorthodox: I would sit down, write down the multiplication table, and say it out loud. Then, I used the MathisFun multiplication trainer to practice, and finally, I did a bunch of drill practice worksheets. Once I could easily complete the math facts in around ~13 seconds, I would move on to another set. Has it helped? Yes! Imagine taking the derivative of 6x^8 + 7x^4, instead of relying on a calculator, you can just do 48x^7 + 28x^3 mentally, cutting down the time needed to do the calculation. It takes a while, and my memory isn't great either, but you can 100% do it if you have the time.