jmc

Let $M$ and $J$ be the ages of Mickey and Jerry, respectively. Then, $300\%$ of Jerry's age is $3J$. Since Mickey's age is 4 years less than $300\%$ of Jerry's age, we have $M=3J-4$. We are given that $M=14$, so $14=3J-4$. Adding 4 to both sides gives $18=3J$, so $J=6$ and Jerry is $\boxed{6}$ years old.