What date does the gemini month start?!

What date does the gemini month start?

i've been searching on the net and have found that the gemini month starts on may 21 or may 22.

i recently found out the birthday of a friend of mine which is may 21 and i cant pin down his star sign.

any help?

any reasons why there's two dates.. or something the like.

Its called being on the cusp!
I was born on the 23rd october so i am either a libran or scorpion,had my chart done and i am a scorpion(which i think i knew!!) You will need to find out what time he was born to clarify i think.