Why are my games taking so long. 8 game years on a large map for a political victory. Am I just not very good? Underaggressive? Or do I need to play on a smaller map?
There's lots of stuff you don't *have* to do in the game that can be time consuming and can make your games run a lot longer. For example, you don't *have* to set up trade routes. You don't *have* to build any starbases (except resource ones). You don't *have* to build defenses around all your planets. You don't *have* to research more than one line of weapons tech. What you can get away with does depend on how many habitables you're playing with, but there's lots of other stuff as well. Regardless of your win goal, keeping your military rating higher than the other races is key. The higher the better.
Also, there are some tricks to speed up those things you have to do. For instance, instead of building a full colonizer for every planet, just plop a starport on an adjacent one and pop out a small or tiny hull with nothing but a colonizer module on it. A similar thing can be done when updgrading resource starbases.
Some things are just fun to do even though they are time consuming. For instance, it's really fun to fully research two lines of weapons tech then switch guns after the AI has put all their effort into defending against your first weapon. But, that takes a number of turns.
Personally, I can get a gig/abun DA game down to 6 years by doing the absolute minumum I need to win. I can get a gig/abun DL game down to 4. But, that's not necessarily the most fun game. Some of the most enjoyable DA games I've had were more in the 8 year range, 6 for DL. I wouldn't be overly concerned that 8 years is too much time to spend on a large map, but if you want to shorten your games, hopefully you found my comments helpful.