Actually, the current age of a plurality of D&D players who also participate in TMP polls is 50-59. These days the average age of people who play the game currently sold as Dungeons & Dragons is much, much younger.
I'm willing to bet the various editions will skew into their own age groups according to the edition corresponding to the player's age at 12-21, with outliers for wargaming hobbyist who were already adults when Gygax and Arneson first began pitching the game among the wargaming community.
So if you were 12-20 in the late 70s, and still play today, you probably play a version of either Original D&D (or a clone) that is, the trio of booklets and supplements first introduced in 1974, OR Advanced Dungeons & Dragons aka "1e" originally published in 1978.
If you were 12-20 in the early 80s and still play, again you are probably playing the "Basic" boxed set editions from Moldvay, Marsh, Cook and Mentzer OR are playing AD&D 1e.
If you were 12-20 in the late 80s and still play, you are probably playing AD&D Second Edition, aka 2e though you might be a holdout for 1e.
If you were 12-20 in the 90s and early 2000's you probably play the first version of Dungeons & Dragons published by Wizards of the Coast the version called 3e or 3.5e or you play the clone, Pathfinder.
Nobody still plays 4e.
If you were 12-20 from 2014 on, you probably play the current WotC/Hasbro edition of D&D, aka 5e.
There is overlap throughout the above.
Well, except for 4e. As I said, nobody plays that. 
(For the record, I am an outlier, as I began at 14 with Holmes Basic and AD&D 1e, but as an adult switched to Mentzer Basic boxed sets.)
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