By Kayla Kibbe Last night, Oscar’s co-host Amy Schumer cracked a joke people have been making for at least a decade or so. “I mean, Leonardo DiCaprio — what can I even say about him? He’s done so much to fight climate change and leave behind a cleaner, greener planet for his girlfriends,” the comedian quipped while co-hosting Sunday night’s event. Schumer knew her joke wasn’t terribly original, sarcastically explaining it back to the audience: “Because he’s older, and they’re younger. You get it.” Again, people have been making some version of this joke for as long as DiCaprio has been old eno…