Old culture buildings and wonders produce more culture, does anyone know how this is worked out?

Ta

I'm not sure what you mean by "Old culture buildings". Do you mean things like Temples and Obelisks? If so, check out the city improvements (http://www.civfanatics.com/civ4/info/improvements/) page here or the Wonders (http://www.civfanatics.com/civ4/info/wonders/) information here.

These pages (and when you mouse-over them in-game) will say something like +1 culture/turn. As your city grows, you will develop culture (you can see that in the purple bar on the city screen). If you open your city screen and mouse-over that bar, I'm pretty sure you can see what all the sources of culture are.

Your city will generally build up culture as long as it exists (although I think it loses culture if it's attacked).

Not sure if that answers your question...

I think buildings over 1000 years old produce double culture. Its something like that.

Breunor

I was wondering if it was time based, turn based, age based or even possibly had something to do with the culture increments (eg poor, growing, infulential etc).

All buildings that generate culture produce twice as much once the building is more than 1000 years old. That's all there is to it.

it may be because you adopted various civics like free speech or built other wonders like hermitage/etc...

Cheers big ears...