diff --git a/c3l_membership/forms.py b/c3l_membership/forms.py
--- a/c3l_membership/forms.py
+++ b/c3l_membership/forms.py
@@ -117,7 +117,7 @@ class MembershipForm(FlaskForm):
         validators=[InputRequired(lazy_gettext("Please select one of the options!"))],
     )
 
-    birthday = DateField(lazy_gettext("Birthday"), validators=[Optional()])
+    birthday = DateField(lazy_gettext("Birthday"), validators=[InputRequired()])
 
     street = StringField(
         lazy_gettext("Nr., Street"),
@@ -151,9 +151,4 @@ class MembershipForm(FlaskForm):
         validators=[InputRequired()],
     )
 
-    minor_member = BooleanField(
-        lazy_gettext(
-            "I am under 18 years of age and have the approval of my legal representative."
-        )
-    )
     submit = SubmitField(lazy_gettext("Become a member"))