How old was Mikhail Gorbachev when he ecame a member of the Politburo ?
Yuri Andropov , Brezhnev 's 68 - year - old successor , was seriously ill with kidney disease when he took over , and after his death fifteen months later , he was succeeded by Konstantin Chernenko , then 72 , who lasted thirteen months before his death and replacement with Gorbachev .