AMC 8 2011 Problem 21

Students guess that Norb's age is $24, 28, 30, 32, 36, 38, 41, 44, 47$, and $49$. Norb says, "At least half of you guessed too low, two of you are off by one, and my age is a prime number." How old is Norb? $\textbf{(A) }29 \textbf{(B) }31 \textbf{(C) }37 \textbf{(D) }43 \textbf{(E) }48$