If I'm remember well the year 1850 is the last which give you a extra bonus for fast victory.
You get points regardless of what year you win (except 2050 A.D., of course). However, in the later stages of the game the bonus is so small. I believe it's 1 point per YEAR remaining until 2050 multiplied by difficulty level. Example: Win at 1950 A.D. 2050-1950=100 X 3 (for Regent) is 300 point bonus. So, on Regent, if it's after 1950 A.D. you get 3 pts/turn, 1750-1950 A.D.(2 years/turn) its 6 pts/turn. If it's say 700 A.D. (10 years/turn), it would be 30 pts/turn. Even though at 700 A.D., you could get a very big bonus, you would actually end up with more points by going all the way to 2050 A.D. (on most maps). This is because with milking you probably make 20+ points/turn. So even though, you lose a little ground prior to 1000 A.D., you will more than make up for that in the 1750-2050 A.D. era.
That is, of course, if you milk properly, by getting max territory and happiness, and irrigating every single tile, having hospitals and marketplaces in every city, etc. The best strategy is to get just under the domination limit ASAP (start out as warmongerer), then switch to builder mode and build (rush buy) all those marketplaces, aqueducts, and hospitals.
Large, Huge, and some Standard maps, you have a much higher scoring possibility by milking. Tiny and small maps it would be smarter to finish the game quick for the bonus, because on the smaller maps, there just isn't enough territory and population to make up for the early win bonus. The highest possible early win bonus on Deity is about 36,000 pts (win at 3950 B.C.). Aeson got 62,000+ pts by milking.