Turn A Gundam, Mobile Suit Gundam: Iron-Blooded Orphans Recommendations
Both series has a main gundam that was created generations before the characters in the story. These gundams are superior in almost every way compared to the other modern mechas in their series and are both piloted by the main protagonists who are on their early teenage years. However, the protagonists are very different from each others in personality such as the protagonist in Iron-Blooded Orphan is stoic child soldier while the one in Turn A is a curious compassionate worker. Both series also has a princess but from different satellites; Iron-Blood Orphans has a princess of Mars and Turn A has a princess of
Both shows involve a young man using a Gundam from a conflict years (or in Turn A Gundam's case, Centuries) ago to fight for an organization. Also, both feature a princess from a planet that isn't Earth.