How to find prime numbers in an array of arrays

I’m trying to create a function to return the prime numbers on the ages in a multidimensional array.
The problem is the function I created is returning only the first occurence and I want it to return all the occurences.

Here it is what I’ve done:

function findPrimes(){
    $people = [
        [
            'name'  => 'Joseph Richard',
            'age'   => 23,
            'city'  => 'Chicago',
            'level' => 'Senior',
        ],
        [
            'name'  => 'John Doe',
            'age'   => 22,
            'city'  => 'New York',
            'level' => 'Pleno',
        ],
        [
            'name'  => 'Tess',
            'age'   => 21,
            'city'  => 'San Diego',
            'level' => 'Junior',
        ],
        [
            'name'  => 'Steph Morgan',
            'age'   => 20,
            'city'  => 'Miami',
            'level' => 'Junior',
        ],
        [
            'name'  => 'Ken Junior Smith',
            'age'   => 23,
            'city'  => 'Los Angeles',
            'level' => 'Senior',
        ],
        [
            'name'  => 'Walter Scott',
            'age'   => 24,
            'city'  => 'Seattle',
            'level' => 'TechLead' 
        ],
        [
            'name'  => 'Diego Maradona',
            'age'   => 25,
            'city'  => 'Austin',
            'level' => 'TechLead' 
        ],
        [
            'name'  => 'Messi',
            'age'   => 26,
            'city'  => 'Portland',
            'level' => 'Pleno' 
        ],
         [
            'name'  => 'Hardin Scott',
            'age'   => 19,
            'city'  => 'Houston',
            'level' => 'Senior' 
        ],
    ];

    $age = array_column($people, 'age');

    foreach ($age as $key => $value) {
        $isPrime = true;
        for($i = 2; $i <= sqrt($value); $i++)
    {
        if($value % $i == 0) 
        {
          $isPrime = false;
        }
    }
        if ($isPrime == true)
        {
            return "$value is prime number";
        }
        else {
            return "$value  is not prime number";
        }
}
}
echo findPrimes();

Output: 23

I need it to return all prime numbers in this array. Can anyone help me please?

>Solution :

Your function is executing a return in the first iteration of the foreach loop. And returning a string like "x is prime number" seems not to be what you want as result (as you say you want a list of primes).

So define an array $primes and populate it with those values that are primes, and return that array.

    // ... after the initialisation ...
    $age = array_column($people, 'age');
    $primes = [];
    foreach ($age as $key => $value) {
        $primes[] = $value; // first assume it is prime
        for($i = 2; $i <= sqrt($value); $i++) {
            if($value % $i == 0) {
                array_pop($primes); // ...then remove it if it's not
                break;
            }
        }
    }
    return $primes;
}

print_r(findPrimes());

Note that since ages are expected to be in the range of 0 to 140, you can predefine a list of all primes less than 140 (with a sieve). Then all that remains is to check if an age is in that list…