The following quote is from Crimhthan_The_Great in the 'Introductions' thread at OD&D Discussion. All emphasis is mine.
My birth year is 1937 and I turned 70 in April of this year. Our original core group of 9 guys all grew up together and we are all within a few years of each others ages. Out of the original 9, 5 of us still live in the same neighborhood and play regularly. The other 4 still show up about 4-6 times a year. They each have their own campaigns.
We started an organized twice-weekly game night in 1956 playing cards, boardgames, and wargames that we made up. We had played together from early childhood (cowboys and indians was a long time favorite), we were into westerns, fairy & folktales, science fiction and alot of other things. I remember homemade bow & arrows, spears, swords, staffs etc., and hunting with our fathers and grandfathers, and getting old enough to get our first guns.
Starting in 1956 (noted above) up until 1971 we had played about 1400 game sessions. Then in early April 1971, a cousin of one of my friends sent him a copy of the Fantasy section of Chainmail. We got hooked on it quickly and played it right up until the same cousin sent a copy of D&D in February 1974 and we immediately converted our Chainmail campaign over to D&D.
Starting with Chainmail Fantasy and continuing with OD&D we played our 1000th gaming session in January of 1982, our 2000th in December 1995 and our most recent was number 2832. One of our goals is to reach 3000 before any of us dies of old age or becomes to senile to play.
We have played through about 284 years of game time in the main campaign and have four OD&D side campaigns in the same world. I call the main campaign the Tarrozian Campaign and it is very deadly. TPK's are common and getting a group of characters to 4th level is always a cause for celebration. I also have two OAD&D campaign which share the same world(but not the same as the OD&D world).
We have dabbled a little tiny bit in Holmes basic, BX, BECMI and the Rules Cyclopedia.
We have played through 284 years of game time in the main campaign and the original core group of players have had between (I am guessing here) 500-700 characters each. In spite of about 350 TPK's, each of us have retired about 10-18 characters apiece. But in some gaming sessions we have went through 8-10 characters each.
(counting from 1956 we are at 4232 gaming sessions, counting from the start of the Chainmail Fantasy (proto D&D) campaign in April of 1971 we are at 2832 gaming sessions as of 06/23/2007)