My 13 y.o. son wanted to download Section 8: Prejudice last weekend because it was very much like Halo but was only rated 12 on the Xbox Live marketplace. Now there is less confusion as PEGI ratings are now implemented in the UK and the BBFC no longer provides ratings for videogames.
I was suspicious because he had downloaded a demo and I couldn't believe it was only rated 12, so I checked the PEGI website and it was rated 16 (also on different consoles). I promptly emailed PEGI and Xbox Live support to inform them, and I have received a reply from PEGI a few minutes ago. They say they will inform Microsoft and ensure that it is corrected there.