The funny thing is, I don't think younger crowds are having as much trouble as some of the old timers enjoying all versions of Trek.
I think that attempting to paint the picture strictly in terms of older age-groups or younger ones simply doesn't work very well.
We've had people in the past who tried to make a case for Abrams' version of Trek as being only for the young, only for the short-attention-span/ADD/MTV/XYZ Generation, etc. and such arguments never really held any water. Pick any age group, and you'll likely find disagreement: some will like all of Trek; some will like only the one they grew up with; some grew up with one series and later became hardcore fans of another series to the exclusion of all else. Even among those who came to Trek only with the 2009 movie there are a wide variety of reactions to the earlier series and movies.