Is he older? He probably feels like he’s falling behind and is, like Matt said, jealous of your Light.

Is he the same age (high school)? Again, panic, but normal sibling rivalry.

Younger? Afraid to see you taken away by interests and then, finally, the Big World.

A counter would be, “I’ve been into Buddhism/whatever before it was cool, where have you been, little brother?” with a head noogie. 😉

Or, “So what are you into?” (not sarcastic, genuine interest)

Or, “Yup, you’re right, I’m an attention whore/whatever… So, Mom, the eight noble paths are..”