I don't know if there's anything to the age thing, but I do have an interesting anecdote that may relate.
Today was the first session of a new 4E campaign. Most of the group just finished playing in a year-long monthly Rules Cyclopedia game with me. Their ages are 8, 9, 9, 9, 37, 41, and 40. We added two new players, who are 12.
We had more shouts of excitement, intent watching of others' turns, and real investment in character-making in that one session than I saw in an entire year of RC. When the wolf-girl rogue finally put down the ogre just before it broke its bonds and charged, with a maxed-out Torturous Strike, we high-fived all round.
So whatever else you can say, I think that the future of D&D is in safe hands with 4E.
I'm 41, and my favorite edition WAS Rules Cyclodedia/Mentzer. I'm solidly in 4E's corner now.