To the OP, Kakashi never said someone couldn't learn all 5, he only said that most Jonin know 2.
Don't forget in the canon anime he used fireball Justus against Sakura and naruto.
Uhm... no that was 100% not canon. He only has Lightning, Water, & Earth.
can you show me a scan, [just need to see], because the one i have seen Jiraya said it was ''Unprecedented'', meaning not done before
1) you shouldn't take direct quotes from a translation too literally.]
2) unprecedented can also mean unparalleled, mean he is the only one who can master all 5 at that level.
3) Juriya could have been considering the age Nagato was when he was able to master all 5.