Nearby Sun-like stars are prime targets of the PLATO mission for the detection and characterization of exo- planets and possibly exo-Earths. Understanding the formation history and determining the age of these sample stars (and their planetary systems) is thus essential. The chromospheric emission in the cores of the Ca II H & K lines of late-type dwarfs is a well-known indicator of magnetic activity that decreases with increasing stellar age. I used this indicator to investigate the formation history of nearby G- and early K-type stars with origins at galactocentric distances similar to that of the region where the Sun was born.