Well, I worked off
http://wiki.battlemaster.org/wiki/Calendar which says that characters age a "year" every 6 weeks. Battlemaster started in 2001/2 from what I'm told, so I presumed that Gregor was roughly nine RL-years old. That works out to roughly 470 weeks, which divided by 6 gives about 78. Round numbers are nice, so I called it 80.