Really?

Why is that when you're trying to tell a story and then mention someone that's "older" than you, some people have to ask, "well what's older?" with a bit of a scoff in their voice. Like they're trying to be sarcastic, but there's that subtle hint of them being offended. Like heaven forbid someone is older than me.
Next time someone older than me tells a story about someone being "younger" than they are, I'll be sure to scoff in a sarcastic, but slightly offended manner. Wonder what kind of reaction I would get...