"The average age of the most frequent game purchaser is 41 years old."
http://www.theesa.com/facts/index.asp
"The average gamer is 37 years old and has been playing for 12 years."
http://en.wikipedia.org/wiki/Video_game
"UK Gamers * The average gaming age is now 23+.
US Gamers * The average game player is 35 years old and has been playing games for 12 years."
http://www.theaveragegamer.com/averagegamers/
It seems to depend on where you are, and who you ask, but I suspect the average gamer is a bit older.