MECCG was built upon a "what if..." universe. Plus the only timetable the authors specified was "the free peoples tried to orginaze to resist to Sauron" (the One Ring isn't even found at the start of the game).
LOTR (Decipher) was based upon the movies, so the timeline was a lot more specified and respected.
LOTR (FFG) is specifying a timeline (between Hobbit and LotR) which is a mistake to me : this will generate subject like this one (isn't Thorin dead at the end of the Hobbit) and brings nothing to the game.
Anyway, I didn't kill my eyes on the appendixes of the LotR book, so I didn't pay attention Eowyn was so youth. And I don't care about this detail, as it won't prevent me from enjoying (or not) this upcoming game.
The bright-side is that we'll play with famous characters (Thorin II) instead of some generic FFG-created "dwarf-lord" with equal stats and role.