Okay, I've looked at starters form generations 1-4 and their personalities and have matched them up with a Western Zodiac sign. This is based upon brief anime observation, Mystery Dungeon tests, and Pokedex descriptions. The times are simplified to the month that dominates the rule of that sign. I like how mine turned out, I saw that Turtwig had a lot in common with Scorpio, so I know some people will be happy. Here we go:
January- Squirtle. Squirtles are rebelious, proud, calm, and their mood changes often. They try to impress people a lot.
February-Cyndaquil. Cyndaquil are timid, kind, and are easy to get along with, unless you're a thrill seeker.
March-Treecko. Treecko like to keep their cool, have good qualities galore, but are less than they think they are.
April-Chimchar. Chimchar are kind of brave, bold, don't take crap from others, and can be good friends if they respect you.
May-Charmander. Stubborn, strong, and interesting friends, they make friendships a lot less boring.
June-Totodile. Happy, energetic, impatient and naive are all qualities of Totodiles.
July-Bulbasaur. Kind, easy-going and cheerful,Bulbasaur are good friends for mild people.
August-Mudkip. Mudkip are calm, adaptable and optimistic in a sense.
September-Torchic. These Pokemon are impatient, happy and proud. They can be sassy quite often.
October-Chicorita. Chicorita are calm (we get that a lot), compassionate, and are loyal friends.
November-Turtwig. Turtwig are lovers of many things, yet very strong. They should not be misinterpreted for their passions.
December-Piplup. Proud, happy and sassy, these Pokemon are fun to be around.