Board Thread:Theories and Speculation/@comment-30323490-20170305205254/@comment-6769189-20170307070248

Everyone has the opportunity to learn Sage Mode. Minato and Jiraiya, who don't have anything in particular special about them besides their own natural high chakra levels, learned it.

High chakra levels fall within the "no outside source" category. Techniques like Raikiri require high amounts of chakra.

The ability to sense, gather, and harness Natrual Energy can be achieved naturally, with ones own skill and hard work. Unlike EMS, Rinnegan, Tenseigan, RinneSharingan, or through implants. Therefore, valid.