One possible explanation for this large difference might be the historically rather repressive attitude towards sexuality in legislation that was the norm in Germany and countries under German influence. This included increases in the age of consent, sometimes to as high as 18 years, which have been only partly reversed in recent decades. Most catholic countries did not experience this and the age of consent has stayed low. Another similar phenomenon is the legal attitude towards homosexuality: it was legalized in the European catholic countries already in 19th century, but in protestant countries only in later 20th century.

Of course official legislation does not necessarily reflect the general attitude towards things. It may be lagging behind, or laws may be liberal but most people prudes. Sometimes laws can be just arbitrary, like in the United States, where age of consent varies from one state to another, sometimes being 16 years and sometimes 18, even though the neighbouring states may be very similar in their values, including prudeness.