I think it was about 2 and a half hours. Depends on what he's like, I took my 12 year old son and his 12 year old mate, they, like me, loved every second of it. I highly recommend it (in 3D). Best trip to the cinema in years, in fact, ever.
Went with my 13 year old son and 9 year old daughter both loved it, she tought it was best film she had ever seen was not bored at all, was best graphics i have ever seen.