We rescued Iris 3 years ago. The conditions were deplorable and our guinea was not socialized, overgrown nails, ill, living in filth, & on their 3rd or more home. Of course we haven't a clue the age. After confidently ascribing the male gender to our Iris we set out to find "him" friends.
Now when we get home introductions couldn't have gone better! Nobody mounted, but my husband now has me concerned. I have once again separated Iris in fear of geriatric conception.
Note: after this picture I cleaned off Iris' bottom, but had difficulties taking a clear picture myself.

Our First Obvious Male

Second of Our New Pre-Bonded Males

Iris, 4 years
Iris looks rather male to me too. Definitely best to keep them separated as