Is extremely young meat indigestible?
I think that the regulation is there to prevent the marketing of meat from stillborn animals or aborted animals. The EU wants animals to be inspected before they are killed and after they have been killed, and it wants the killing process to be done under certain conditions.
Obviously a stillborn/aborted animal does not satisfy these requirements.

And an animal that has been killed while very young may be hard to tell from an aborted one.