While I was looking around at interviews, I came across this interesting tidbit. In the May Newsorama.com interview, Jeffrey says, when talking about fan interpretations of Cecil, “But people don’t have to limit Cecil to a certain visual, or body type, or even gender.”
It’s pretty well known in the fandom that Cecil’s race and size are open to interpretation, but there aren’t a ton of headcanons that take this into account. While I’m pretty sure Cecil has accepted (or at least not objected to) he/him pronouns in the show, it is entirely possible that he doesn’t identify as male.
EDIT: Here’s a link to said interview