Laravel: Middleware

En la consola:
php artisan make:middleware MiPropioMiddleware

Añadir en App/Http/Kernel.php:
protected $routeMiddleware = [
...
'es_mayor_de_edad' => \App\Http\Middleware\MiPropioMiddleware::class,
]

Editar tu App\Http\Middleware\MiPropioMiddleware.php:
public function handle($request, Closure $next)
    {
        if ($request->input('edad') < 18) {
            return redirect('home');
        }
        return $next($request);
    }

En ClienteController.php:
public function __construct() {
    $this->middleware('es_mayor_de_edad', ['only' => 'store']); // que solo se ejecute para el método store
}