- According to Kakashi, every ninja has the potential to master the elements. This includes even the fodders, and this includes everyone who has average chakra control.
- According to Tsunade and Shizune, the Yin seal can't be mastered without perfect chakra control
So this means if someone wants to master the Yin seal, at first he has to PERFECT his chakra control ( which is nearly impossible ), then he needs 3 years to fill the seal.
If even Shizune, a top tier medical ninja with precise chakra control, wasn't able to master it, then I bet it can't be mastered by every random fodder.
- mastering the elements only requires time, mastering the Yin seal requires perfect chakra control AND time.
Hiruzen could never master the Yin seal because nothing suggests his chakra control is as good as Tsunade's or Sakura's, but Tsunade or Sakura could easily master the elements due to their perfect chakra control.