In a regular hexagon, the area of $\triangle ACE$ is formed by drawing diagonals between alternate vertices. The area of this triangle is a part of the entire hexagon, which can be divided into 6 equilateral triangles. Each triangle has an area that is $\frac{1}{6}$ of the total hexagon area.
Since the triangle $\triangle ACE$ covers two of these smaller triangles, the area of $\triangle ACE$ is $\frac{2}{3}$ of the total hexagon area.