Hi,
I considering the same trip, mainly because it covers both christmas and new year.
For the record I'm 54 and on the JY holidays I've done so far ages have ranged from late 20's to 80, usually a good mix. I'll add the majority seem to be in their 50's and 60's but i've found everyone gets on.
I've done only one christmas hol (last year) and found the average age was much higher than normal but that was a coach holiday and think that was more the reason than it been christmas, but not sure.
You could use the "ask the editor" part of this forum and Ben will tell you the age range booked so far.
Mick