here is what i got for ya:
There is no direct way for you to tell whos the oldest or whos still active. character employment history works as a marker of date of birth for younger toons, like me. but no such info exists on the old toons bios till they joined their first player run corp and/or the employment history bug was fixed. So we'll have to look at it indirectly and come to some conclusions...
I'm told that all of the final beta toons were killed and players had to make new toons when the doors officially opened in may 03.
This is a link to a CCP dev blog by CCP Oveur from 04 on EVE's first 10s. It shows Dagny as the first toon created. Now, I'm unsure on any means to determine exact activity on a toon. however, Dagny was active enough to change corps in the summer of 2010. and, the toon shows killboard activity via battelclinic this summer. So, if CCP says Dagny was the first live toon then hes a good candidate to be the oldest active toon.
If Dagny isn't active any more another possibility is Wiziwig. Hes on the list and i know was around back in 09 trying to get his test server account reactivated. Hes still the CEO of a 5 man corp but i cant find any activity for the toon online since then to cite.
Still another possibility is Zeus. hes also mentions as one of the first ten toons that were still alive at the end of the first year of EVE. hes been with the corp Evolution forever and hes always been active. and he was active on the battleclinic killboards and on the EVE forums as recently as June 2010.
Of note, a similar question was posed on the EVE forums just a few weeks ago. therein are more first day/first month toons that seem very alive. The thread suggest that the user ID number in the API is indicative of the order that the toons were brought to life in the EVE servers. which makes sense.
ok, I'm done doing research on this subject. I hope something in here fits what you were looking for!