Have you ever wanted to know how long is your friends playing? or how long is the noob that spamming you to invite him to your guild played? Judge the skill!
(READ: This is only work on characters that made AFTER blizzard uploaded the "Achivements/Statistics" to the game! KEEP IN MIND! Its count only the amount played with the character you've checked! if the player has more than one player then you should check his alts aswell for the correct amount!) Anyhow its max the amount he played with the character class forsure!
As simple as can be! Just go to some random in dalaran or who ever talking to you then follow and check his achivement:
Achivement > Statistic > Wealth
Then take a collector and set inside the number you see at "Total gold acquired" for example its 10000 gold then split the number with the number you see at "Average gold earned per day" for example 100 gold and tada! you find out hes played only 100 days! damn newb!
Remmber, do not bother to count silver/copper since its wont change much, maybe hour or 2 and make the collection harder, if you want the 100% amount then do so with "dot" after gold and "dot" after silver
The reason you wont find out the correct amount if he is older than the day the achivements came is: because the gold havnt been collected before then and you cant never know how much he played before it but you do able to know how much he played since then which is atleast 2 years! must have some skill i guess?:P
Have fun finding out how newbs are your guild partners or even leaders to laugh at them or feel like "how the **** they lead me and i played more! SHIT! I AM SO LOSER!" :confused: