You have to tell them your age at some point. In Germany there are restrictions in place to protect minors disallowing them to do certain kinds of works and res

You have to tell them your age at some point. In Germany there are restrictions in place to protect minors disallowing them to do certain kinds of works and restricting when and how long they are allowed to work. You really don't want to break those laws and not just due to legal repercussions. I would be very much surprised if the situation would be significantly different in other (civilized/industrialized) nations.