если нужна только дата
man=Array();
man[0]=Array();
man[0][0]="30";
man[0][1]="40";
man[0][2]="50";
man[0][3]="12/02/1994";
man[0][4]="40";
//---------------------------------------------------------
man[1]=Array();
man[1][0]="20";
man[1][1]="31";
man[1][2]="31";
man[1][3]="12/02/1991";
man[1][4]="31";
//---------------------------------------------------------
man[2]=Array();
man[2][0]="123";
man[2][1]="123";
man[2][2]="51";
man[2][3]="12/02/1971";
man[2][4]="87";
//---------------------------------------------------------
man[3]=Array();
man[3][0]="22";
man[3][1]="56";
man[3][2]="1000";
man[3][3]="12/02/1912";
man[3][4]="100";
alert(man.map(a => a[3].split('/').reverse()).sort()[0].reverse().join("/"));