Both focus on a set of roommates during college. Each have characters with distinct personalities, problems they face, and romances. The relationships built between the roommates in Age of Youth feel similar to the ones of Exclusive Memory.
Also, both have some really cute romance!

Both involve bringing justice for the people, and involve a bit of romance. Personally, both of the weak points in both of these dramas are the romance.

The two dramas have different dynamics. Emperor: Owner of the Mask involves the people & the palace versus the Pyungsoo group. Rebel: Thief Who Stole the People involves the rebels and the palace.

Both place the focus onto the main character who develops into a true leader.