My sister is, or claims to be asexual. I haven't really ever had the chance to talk to her about it though, because she's a little sensitive about it. She's 18 this month, but she hasn't ever dated anyone (although of course this is not uncommon in non-asexual people of that age) and she doesn't ever say: "Ooh x is good looking". It's hard to describe, because written down it just sounds pretty normal, and just like how you might also behave if you just normally keep quiet about these kind of things; but I'm not sure how to describe it.. she just doesn't really think of others as potential partners at all, in any situation.