<?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();
echo $obj->createRandomDate(2015,5,25);