You can go into your battle.net account and look at your subscription history. It goes all the way back to the first day you played/activated play time

/played is pure masochism and I refuse to participate (publicly).

If you're interested in how old your characters are, you could try calculating their age from the quest statistics (found in the achievement window):
Total quests completed / avg. quests completed per day = character's age in days.
It's not super reliable, since average quests may be very low (and thus imprecise) for old characters that haven't done many quests. Plus the statistics window was added in wrath (don't know if the statistics are from before or not?).

If you're lucky, someone with a census addon may have spotted you and you can find your character on https://www.warcraftrealms.com/ . It's pretty cool and lets you trace the history of your characters. Note that if you server/name changed and another character has taken your old name since then they will have overwritten the previous records.

Managed to find this. Musmatta was my 2nd main character, which I still have on my retail account. I made it after my first one (undead warlock, which I cant find) was permabanned after I used some speedhacking stuff, oh those blunder years :)
I remember being level 54 on my warlock when TBC released so I guess I started playing around summer -06