At a guess... I'd say at least 3200. There's a lot of very vague history with very little in the way of date references that's mentioned in various places. For example, there was the war between the GMG and Rheinland, that seems to have resulted in a terrible defeat for Rheinland (and yet, the GMG is one of the lesser Powers, which makes very little sense, considering they control one of the most precious things in the FL universe- H-Fuel).

Liberty is very weak, militarily, because Rheinland and Kusari imposed a terrible peace treaty on them after they tried to fight a war without adequate H-Fuel supplies. Which is why all of their stuff sucks, apparantly.

And there are lots of other things, like the tales told by the Outcasts, which suggest that people have been in Sirius for a very long time.

3101-3200. 24th century = 2301-2400 A.D. 2301 + 800 = 3101

then give or take 50 years on that 800 years thing....

3051-3250 A.D. Now we all honestly know that it's never going to really happen don't we?

You better not touch that button.
*touch*
Great, you just deleted the best mod ever.
What mod?
Too late now. You deleted it.