WALL-E had been cleaning Earth alone for 700 years before meeting EVE.
The film begins in the 29th century, after humanity has abandoned a garbage-covered Earth. Buy n Large left fleets of trash-compacting WALL-E robots behind as part of an attempted cleanup operation, but nearly all of them eventually stopped functioning. The remaining active unit continued compressing and stacking waste without human supervision.
That long isolation explains why this WALL-E develops an unusual personality. He collects objects from the ruins, watches fragments of the musical Hello, Dolly!, and keeps a cockroach named Hal as a companion. His routine changes when EVE, an advanced probe sent from the starliner Axiom, arrives to search for evidence that Earth can support life.
The figure is sometimes paraphrased as “about 700 years,” but 700 is the film’s canonical rounded time span. It describes WALL-E’s lonely cleanup era, not EVE’s age or the exact duration of every robot’s operation.