Nervous about taking Jujitsu?

Well, I'm 13 and i'm starting Jujitsu next Monday. My older brother (16) has been taking Jujitsu for about 6 weeks so far and he says the class is mostly 15-16 year olds,even though they say they don't pair brothers together I'm still worried about getting choked out by some 16 year-old. Any advice?