30年後の日付を取得する方法
($year,$month,$day) = (localtime)[5,4,3];
$after30years = sprintf('%04d-%02d-%02d',1900+$year+30,$month+1,$day);

1000日後の日付を取得する方法
($year,$month,$day) = (localtime(time+1000*24*60*60))[5,4,3];
$after1000days = sprintf('%04d-%02d-%02d',1900+$year,$month+1,$day);