<?php

class RandomDate {
    protected $date;

    public function createRandomDate(int $year = 2007, int $mounth = 1, int $day = 1)
    {
        $randDate = strtotime(rand($year,2017).rand($mounth,12).rand($day,31));
        $this->date = date('Ymd', $randDate);
        return $this->date;
    }
}

$obj = new RandomDate();
$obj2 = new RandomDate();

$some1 = new DateTime($obj->createRandomDate(2015,5,25));
$some2 = new DateTime($obj2->createRandomDate(2012,1,20));

echo $some1->format('Y.m.d');
echo "<br>";
echo $some2->format('Y.m.d');
echo "<br>";
echo "<br>";

if ($some1 > $some2 ) {
    $interval = $some1->diff($some2);
    print_r("Лет: ". $interval->y);
    print_r('<br>');
    print_r("Месяцев: " .$interval->m);
    print_r('<br>');
    print_r("Дней: ". $interval->d);
    print_r('<br>');
    print_r('Дней прошло: ' . $interval->days);
} elseif ($some1 < $some2) {
    $interval = $some2->diff($some1);
    print_r("Лет: ". $interval->y);
    print_r('<br>');
    print_r("Месяцев: ".$interval->m);
    print_r('<br>');
    print_r("Дней:". $interval->d);
    print_r('<br>');
    print_r('Дней прошло: '. $interval->days);
}