It's not age that is really the issue. It's the maturity level. Most students are given this piece and they can't even count correctly yet, or keep a steady tempo, and these are basics. There are too many new techniques introduced within this piece for the average student to handle, and they end up hacking the music to death because of these difficulties. How many times have you heard even the first phrase played in correct time? Think about the masterclasses in which you've seen this piece performed. How many of the clinicians could spend the entire time on the first page, even the first line of music, all the while simply teaching them how to count? It is only assigned because of its familiarity, not its pedgogical possibilities. It is being assigned out of tradition. I'm all for challenging the student, but within reason.
Obviously, this is my opinion and only that. Feel free to disagree.
Robert Henry