ESRB and PEGI
Well, it's age rating is 15 from BBFC and 18 from PEGI. So depending on what store you get it from, it can vary. But if you're getting it from a UK store it is most likely to be 18.
16 +
t for teen
The lowest age rating on a Halo game is "T" for "Teen" (13+), which is the rating for Halo Wars. It was released in March 2009, exclusively for the Xbox 360 console. All of the other Halo games are rated "M" for "Mature" (17+).
ESRB rated it: T(teen) PEGI's rating was: 16
PEGI 16
Pegi-rating is an easy-to-read graphical system used to rate video games for age appropriate content across Europe.
PEGI 16+.
Halo: Reach has a PEGI rating of 16.
PEGI 18+.
PEGI rated it 12+
ESRB and PEGI
It is rated 16+, however I do not believe that this age rating is to stop you from buying the game, just to warn that it may be offensive to some.
No The PEGI (Pan European Games Information) ratings are 3, 7, 12, 16 and 18
The ESRB rating is Mature. The PEGI rating is 18. The BBFC rating is 15.
Just check the ESRB or PEGI rating.