How old were Ed and Al when they performed the human transmutation? How old were Edward and Alphonse when they performed human transmutation? I am referring to the Brotherhood series, not the 2003 version.
Brotherhood more or less follows the manga. I don't remember if we get a montage of events in the brothers' childhoods with their ages (a quick search through volume 6 doesn't give me anything), but we do see Mustang arrive at Resembool presumably shortly after their human transmutation attempt, so we can get some information from there.



So Edward is at most 11, and Alphonse 10, when human transmutation is attempted. This matches up more or less with the ages I remember possibly having seen from 2003 and Brotherhood. (Keep in mind that some chronology - such as the death of Winry's parents - might have occurred at a different point in the manga continuity compared to that of 2003, and that there is the additional half year before Ed takes the State Alchemist exams.)