I think what also bothers me is that my sister is 18. I just feel like it's an automatic no-no to date one of her friends and, well, this girl is my sister's age... so to my mind it's not too far off from actually being the situation where I'm dating someone who's related to my sister in some way, shape or form.
"It is the mark of an educated mind to be able to entertain a thought without accepting it" ~ Aristotle