Prophecy mock all object's methods

I'm using Prophecy in my unit test, I want to mock all methods in user object

class User {


public function age()
{
    return date("Y") - $this->born();
}

public function born()
{
    // Database call or anything else, it's a black box !
}

}

I want to test my the age when the method born changed

    public function testProphecyAge()
{
    $user = $this->prophesize(User::class);

    $user->born()
        ->willReturn(2018)
        ->shouldBeCalled();

    $user = $user->reveal();
    $this->assertEquals(1, $user->age());
}

I get the error

Prophecy\Exception\Call\UnexpectedCallException: Unexpected method call on Double\User\P1