I watched the video a few times and think the "he" pronoun is correct. There are no external distinguishing trait for a female but the male O. briareus will curl the third right arm (clockwise as you orient your eyes with the animal's). Bob does not keep his arm tighly curled enough to be be sure and is moving too fast to see the associated channel but he does seem to keep the tip of the third arm curled while the other arms are straight. Here is a thread that discussed the hectocotylus along with photos of the external identifying male traits.
Guessing an age is never reliable but I believe Bob is a couple of months older than Shiitake but still young. We have unofficially noted a "dent" that appears at the back of the mantle at about 7 months (guessing on timing here) and I see only a suggestion of that dent on Bob so best guess is 5-7 months old. This is a good age as, if I am close, he will be entering his predator vs prey age and should be more willing to be seen than a younger animal.
Guessing an age is never reliable but I believe Bob is a couple of months older than Shiitake but still young. We have unofficially noted a "dent" that appears at the back of the mantle at about 7 months (guessing on timing here) and I see only a suggestion of that dent on Bob so best guess is 5-7 months old. This is a good age as, if I am close, he will be entering his predator vs prey age and should be more willing to be seen than a younger animal.