This is 11:58 again, somewhat amending what I said about the rankings. Interestingly, the graph on Namevoyager also shows that the ranking of Micah is much higher as a boy's name than a girl's name, but that there are slightly more girl Micahs per million babies than boys.
http://www.babynamewizard.com/voyager#prefix=micah&ms=false&exact=true
I am not sure why that is. Maybe it means the top-ranked boys' names take up a bigger chunk of the boys' name market than the top-ranked girls' names, so a girls' name in the 900s is actually given as frequently as a boys' name in the 100s?
Anyway, that argues for Micah being somewhat more ambiguous gender-wise than I thought. But I would not hesitate to name a boy that, given it is still fairly popular as a boys' name and that the Biblical Micah was male.