How many plants do you know that absolutely 100% show their sex after
30-40 days of 6-hour nights? Last time I checked, cannabis either needs
much longer nights or
a lot more than 35 6-hour nights in order to go into the pre-flowering stage.
....and I forgot how hard it is to keep a weed-plant growing for another month or two. It's most likely possible for this guy to either move the plant to another room or section it off (if he even has more than this plant), if he really thinks it's a male.
....I'm not saying it's definitely a male or a female, I'm saying it's too early. And if it is possible to temporarily move it, than that's obviously the safest choice. If you think it is a male, than say that. But don't push the man to kill his plant, that's his decision.