How many times have you heard this line? "Oh, you're too young to know you're not interested in romances/sex." Funny, the first time I heard about sex, I was stricken. I remember thinking, is that really what I have do to in the future? The good thing is, you don't have to have sex if you don't want to! But it doesn't stop people, even well-meaning people, from discounting the experiences of ace people.
Here specifically, I wanted to show that Osiris isn't being intentionally mean, but rather ignorant. In the world of HoT, most gods are very interested in romance and sex. The thought that some mortals aren't confuses them. But his words really didn't do him any favors with Cyrus.