I'm definitely NOT an authority, but it may be a female based on the more rounded dorsal fin. I believe male Geos have more of a curve or "swoop" to their dorsal fin.....but let's wait for some more experienced opinions!
Male Geos have blue iridescent lines on their cheeks while the females have spots. Male dorsal fins are more pointed and females are rounded (just like flicka said), (but then there is the venting part, which can be very tricky). It looks like it can be a female, male dorsals also have long flowing dorsals aside from the pointed part.