ITs not really about ranks, I believe. Check out Naruto he summoned Gamabunta right off the bat, and Gamabunta is one of the strongest Toads. All it takes is chakra and learning how summon them. Naruto was a Genin and he summoned one of the strongest Toads.Ppl
as much as i remember
there r ranks in summoning frogs
one cannot summong all frogs immediatly
when they grow stronger they can summon stronger frogs
naruto is stronger than jiraiya (next generation surpasses the previous)
so he can summon stronger frogs and more of em at same time probably to