1. 'Less than ten years old' is fine. The word 'less' is referring to the age of the bridge - a figure ( < 10) - not the individual years. You can say 'fewer than ten years old' if you want, but making a point of changing from one to the other strikes me as pedantic. 2. It's hard to say without seeing the context. There is no difference between BE and AE in the way we use the past perfect/past simple, but the overuse of the past perfect is generally seen as clumsy and poor style. Perhaps the American adapter thought the past perfect was unnecessary and changed to a straightforward past simple as a stylistic improvement. Whenever I've had occasion to read these books aloud, I've found JKR's style to be rather clunky. One way of remedying this is to remove redundant past perfects. 3. This is a question I'd like to ask American readers. Has anyone any idea why the US version changed 'called' to 'named'? As in 'a woman called Narcissa' being changed to 'a woman named Narcissa'? Can't 'called' be used in this way in AE? The Amazon link takes you to a US site, so the version is very likely to be the US one.

None of it makes much sense to me. The differences in UK and American English amount to 28%, but these occur in pronunciation, spelling, and word usage. Differences in grammar are minuscule.

You think that is bad, in the Italian version most of the names have changed and they use the "past historic" throughout (a tense that is only used in literature and Tuscany) :-)