Can you recomend older cars for a daily driver?

Hello, I'm 23 and considering buying my first own car on the future. I'm looking for something older (definetly before euro 6 rules for diesels since 2015), diesel, fuel efficient and on the smaller side, preferably automatic.

How old could it be? guess galvinized would be preferable to non galvinized for rust issues. What should the maximum kilometrage be? What kind of gearboxes to prefer/not to, for automatics?