diff --git a/src/Form/Service/ParticipantFieldOptionsProvider.php b/src/Form/Service/ParticipantFieldOptionsProvider.php
index ef3d1b4..866595f 100644
--- a/src/Form/Service/ParticipantFieldOptionsProvider.php
+++ b/src/Form/Service/ParticipantFieldOptionsProvider.php
@@ -191,11 +191,18 @@ class ParticipantFieldOptionsProvider extends AbstractFieldOptionsProvider
 
                     $attributes = [];
 
-                    // Make readonly and checked for mandatory services (pre-selection handled by service layer)
+                    // Make mandatory services readonly only when actually selected by participant.
+                    // Unselected mandatory services remain interactive so the user can select them
+                    // after age changes (e.g. agency skeleton bookings where DOB is corrected).
                     if (true === $service->mandatory) {
-                        $attributes['checked'] = true;
-                        $attributes['readonly'] = true;
-                        $attributes['data-tooltip'] = 'Diese Leistung ist nicht abwählbar';
+                        $participant = $bookingDto->getParticipant($participantIndex);
+                        $isSelected = null !== $participant
+                            && $this->hasServiceById($participant->additionalServices, $service->id);
+
+                        if (true === $isSelected) {
+                            $attributes['readonly'] = true;
+                            $attributes['data-tooltip'] = 'Diese Leistung ist nicht abwählbar';
+                        }
                     }
 
                     // Add service description as data attribute for frontend use
diff --git a/tests/Form/Service/ParticipantFieldOptionsProviderMandatoryServiceTest.php b/tests/Form/Service/ParticipantFieldOptionsProviderMandatoryServiceTest.php
new file mode 100644
index 0000000..48e54b7
--- /dev/null
+++ b/tests/Form/Service/ParticipantFieldOptionsProviderMandatoryServiceTest.php
@@ -0,0 +1,151 @@
+<?php
+
+declare(strict_types=1);
+
+namespace App\Tests\Form\Service;
+
+use App\BusProNet\Constants;
+use App\BusProNet\Model\Service;
+use App\BusProNet\Model\Travel;
+use App\Form\Model\BookingDto;
+use App\Form\Model\ParticipantDto;
+use App\Form\Service\ParticipantFieldOptionsProvider;
+use App\Service\BookingPriceCalculatorService;
+use App\Service\InsuranceService;
+use App\Service\ServiceAvailabilityCalculator;
+use PHPUnit\Framework\TestCase;
+use Symfony\Contracts\Translation\TranslatorInterface;
+
+/**
+ * Tests that mandatory services in choice_attr are only locked (readonly)
+ * when actually selected in the participant's DTO, preventing incorrect
+ * force-locking after age-related service changes.
+ */
+class ParticipantFieldOptionsProviderMandatoryServiceTest extends TestCase
+{
+    private ParticipantFieldOptionsProvider $provider;
+
+    protected function setUp(): void
+    {
+        $serviceAvailabilityCalculator = $this->createMock(ServiceAvailabilityCalculator::class);
+        $insuranceService = $this->createMock(InsuranceService::class);
+        $priceCalculatorService = $this->createMock(BookingPriceCalculatorService::class);
+        $translator = $this->createMock(TranslatorInterface::class);
+
+        $this->provider = new ParticipantFieldOptionsProvider(
+            $serviceAvailabilityCalculator,
+            $insuranceService,
+            $priceCalculatorService,
+            $translator
+        );
+    }
+
+    public function testMandatoryServiceSelectedHasReadonlyAndTooltip(): void
+    {
+        $mandatoryService = $this->createMandatoryService(1, 'Ortstaxe');
+        $travel = $this->createTravelWithAdditionalServices([$mandatoryService]);
+        $bookingDto = new BookingDto($travel, 1);
+
+        $participant = new ParticipantDto();
+        $participant->index = 0;
+        $participant->dateOfBirth = $travel->dateFrom->modify('-25 years');
+        $participant->additionalServices = [$mandatoryService];
+        $bookingDto->participants[0] = $participant;
+
+        $options = $this->provider->getFieldOptions('additionalServices', $bookingDto, 0);
+        $choiceAttr = $options['choice_attr'];
+        $attributes = $choiceAttr($mandatoryService);
+
+        $this->assertTrue($attributes['readonly']);
+        $this->assertSame('Diese Leistung ist nicht abwählbar', $attributes['data-tooltip']);
+        $this->assertArrayNotHasKey('checked', $attributes);
+    }
+
+    public function testMandatoryServiceNotSelectedHasNoReadonlyOrChecked(): void
+    {
+        $mandatoryService = $this->createMandatoryService(1, 'Ortstaxe');
+        $travel = $this->createTravelWithAdditionalServices([$mandatoryService]);
+        $bookingDto = new BookingDto($travel, 1);
+
+        $participant = new ParticipantDto();
+        $participant->index = 0;
+        $participant->dateOfBirth = $travel->dateFrom->modify('-25 years');
+        $participant->additionalServices = [];
+        $bookingDto->participants[0] = $participant;
+
+        $options = $this->provider->getFieldOptions('additionalServices', $bookingDto, 0);
+        $choiceAttr = $options['choice_attr'];
+        $attributes = $choiceAttr($mandatoryService);
+
+        $this->assertArrayNotHasKey('readonly', $attributes);
+        $this->assertArrayNotHasKey('checked', $attributes);
+        $this->assertArrayNotHasKey('data-tooltip', $attributes);
+    }
+
+    public function testNonMandatoryServiceUnaffected(): void
+    {
+        $nonMandatoryService = new Service();
+        $nonMandatoryService->id = 2;
+        $nonMandatoryService->label = 'Keycard-Pfand';
+        $nonMandatoryService->subType = Constants::TOKEN_ADDITIONAL;
+        $nonMandatoryService->available = 10;
+        $nonMandatoryService->price = 10.0;
+        $nonMandatoryService->mandatory = false;
+
+        $travel = $this->createTravelWithAdditionalServices([$nonMandatoryService]);
+        $bookingDto = new BookingDto($travel, 1);
+
+        $participant = new ParticipantDto();
+        $participant->index = 0;
+        $participant->dateOfBirth = $travel->dateFrom->modify('-25 years');
+        $participant->additionalServices = [$nonMandatoryService];
+        $bookingDto->participants[0] = $participant;
+
+        $options = $this->provider->getFieldOptions('additionalServices', $bookingDto, 0);
+        $choiceAttr = $options['choice_attr'];
+        $attributes = $choiceAttr($nonMandatoryService);
+
+        $this->assertArrayNotHasKey('readonly', $attributes);
+        $this->assertArrayNotHasKey('checked', $attributes);
+    }
+
+    public function testNullParticipantReturnsEmptyOptions(): void
+    {
+        $mandatoryService = $this->createMandatoryService(1, 'Ortstaxe');
+        $travel = $this->createTravelWithAdditionalServices([$mandatoryService]);
+        $bookingDto = new BookingDto($travel, 1);
+
+        // Do not set participant — age filtering cannot determine choices, returns empty
+        $options = $this->provider->getFieldOptions('additionalServices', $bookingDto, 0);
+
+        $this->assertEmpty($options);
+    }
+
+    private function createMandatoryService(int $id, string $label): Service
+    {
+        $service = new Service();
+        $service->id = $id;
+        $service->label = $label;
+        $service->subType = Constants::TOKEN_ADDITIONAL;
+        $service->available = 10;
+        $service->price = 5.0;
+        $service->mandatory = true;
+
+        return $service;
+    }
+
+    private function createTravelWithAdditionalServices(array $services): Travel
+    {
+        $travel = new Travel();
+        $travel->dateFrom = new \DateTimeImmutable('+30 days');
+        $travel->dateTo = new \DateTimeImmutable('+37 days');
+
+        $indexed = [];
+        foreach ($services as $service) {
+            $indexed[$service->id] = $service;
+        }
+        $travel->additionalServices = $indexed;
+
+        return $travel;
+    }
+}