Sexual Offences (Northern Ireland) Order 2008
The Sexual Offences (Northern Ireland) Order 2008 was an Order in Council by the UK Government, which completely overhauled the law relating to sexual offences in Northern Ireland. Amongst many other changes, it lowered the age of consent to 16.
http://www.legislation.gov.uk/nisi/2008/1769/contents Text of the Order
http://www.nio.gov.uk/explanatory_guidance_to_the_sexual_offences_%28ni%29_order_2008.pdf Northern Ireland Office: Explanatory Guidance