Without the age restriction, there would be $\binom{6}{3}\binom{7}{4}$. Of these, exactly $\binom{5}{2}\binom{6}{3}$ are illegal due to featuring the youngest member of each sex. This makes the number of legal solutions $\binom{6}{3}(\binom{7}{4}-\binom{5}{2})=20\times (35-10)=500$.