Validation for Birth date >49 at Model level or xxx.ctp or even Controller?

In Model/table we have a membres.php with that statement:
$validator
->date(‘date_de_naissance’)
->requirePresence(‘date_de_naissance’, ‘create’, ‘Une date de naissance est requise.’)
->notEmpty(‘date_de_naissance’, true, ‘La date de naissance ne peut pas être vide.’);
we want to add extra validation for date_de_naissance > 49.
And at entry level (template): filename.ctp:

<?= $this->Form->control('date_de_naissance', ['label' => 'Date de naissance', 'required' => true, 'monthNames' => $mois, 'minYear' => 1900, 'maxYear' => date('Y')]) ?>

Please help
New in CakePHP but enthusiastic

if i understand correctly you only give year to validate so maybe something like this

use Cake\I18n\Date;

...

$atLeast49 = (new Date())->subYears(49)->year;

$validator
       ->lessThan('date_de_naissance', $atLeast49, 'Too young.');