Kirin-mo Oitewa Doba-ni Otoru (きりんもおいてはどばにおとる)
= A genius grown old becomes worse than mediocre.
Kirin (Kilyn): <art> A fiery horse (imaginary creature) drawn on Japanese or Chinese ceramic ware. Usually it is considered as a superior creature like a unicorn in Western World.
Oitewa (Oiru): get old + -tewa (if you get old…)
Doba: a hack; a jade; a worn-out horse
Otoru: be inferior to; be worse than
A genius cannot be a genius for the rest of his life.