I have different interpretation of being a genius. Being a genius doesn't mean she or he can solve really hard problems easily. One is a genius if he or she does solve really hard problems, especially in the fields like math, physics, etc. where all low-hanging fruits were way gone. Both Zhang and Perelman are genius, in my eyes. It doesn't matter how long it takes one to solve the hard problems. It sounds a fairy tale to me that someone wakes up one day with a genius thought, and two weeks later, complete a solution for a really hard problem in math, physics, etc. in nowadays.