The guy sounds very similar to me at work and I'm an Aqua, looks are completely different though. I'm aqua with saggitarius rising and Libra moon. So as an alternative I'd go Libra or GEMINI with something aquarian thrown in to the mix.
You could always cheat if he is so open and helpful. I've got to buy my girlfriend a birthday present soon, its ages until my birthday, whens yours? Or some other subtle ploy to find out his birthdate. Saves all this guessing business.
Oops, from his appearance and overtly caring/helpful attitude I'd go cancer - maybe as a rising (ascendant) sign.
That type of socially interactive personality sounds like a Libra but leans towards one of the fire signs too (because of his outgoing personality)... Sag, Leo or Aries. Taureans are also very popular amongst people but not that outgoing.