Board Thread:Versus Debates/@comment-30830650-20170116074632/@comment-9782468-20170119061232

Jiraiya can maintain Sage Mode until his own chakra runs out, since the Nature Energy is being gathered for him while he fights. Naruto couldn't because he had to stay absolutely still.

However, if Jiraiya doesn't have enough of his own chakra to balance with Nature Energy, he can't go Sage Mode. He'll turn into a Toad statue because he won't be able to balance the chakra properly.

EDIT: to be more clear, Ma and Pa gather Nature Energy for him while he fights, but he's the one balancing the Nature Energy with his chakra to make Sage Chakra. If he doesn't have enough chakra to balance with the Nature Energy Ma and Pa gathers for him, then his chakra and Nature Energy will be unbalanced, petrifying him.