Somebody knows when it is the birthday of K1, in the series it seems to be that it is mentioned that his sign Capricorn, but never I have seen that they mention the day and the month like with the goddesses:inoc: who know???

Jan.1, 1969 - as per Fujishima-san. Same goes for bell.

They may disregard the year if it's every mentioned again. Since using real time that would make him 37 years old.