Here is my solution with getters and setters:

<?php
 
class Student
{
    private $firstName;
    private $lastName;
    private $age;
    private $city;
 
    /**
     * @param mixed $firstName
     */
    public function setFirstName($firstName): void {
        $this->firstName = $firstName;
    }
 
    /**
     * @param mixed $lastName
     */
    public function setLastName($lastName): void {
        $this->lastName = $lastName;
    }
 
    /**
     * @param mixed $age
     */
    public function setAge($age): void {
        $this->age = $age;
    }
 
    /**
     * @param mixed $city
     */
    public function setCity($city): void {
        $this->city = $city;
    }
 
    /**
     * @return mixed
     */
    public function getFirstName() {
        return $this->firstName;
    }
 
    /**
     * @return mixed
     */
    public function getLastName() {
        return $this->lastName;
    }
 
    /**
     * @return mixed
     */
    public function getAge() {
        return $this->age;
    }
 
    /**
     * @return mixed
     */
    public function getCity() {
        return $this->city;
    }
}
 
$command = readline();
$students = [];
 
while ($command !== "end") {
    $fields = explode(" ", $command);
 
    $newStudent = new Student();
    $newStudent->setFirstName($fields[0]);
    $newStudent->setLastName($fields[1]);
    $newStudent->setAge($fields[2]);
    $newStudent->setCity($fields[3]);
 
    $students[] = $newStudent;
 
    $command = readline();
}
 
$city = readline();
 
foreach ($students as $student) {
    if ($city == $student->getCity()) {
        echo $student->getFirstName() . " " .
            $student->getLastName() . " is " .
            $student->getAge() . " years old." .
            PHP_EOL;
    }
}