Andrew thinks that all young people are irresponsible, and are always late for work. They don't meet their deadlines, don't take things seriously, and are always carefree. This type of perception is called as Stereotyping .
Andrew has fixed this image in his mind and always associates it with young people.
We can understand the concept through some common examples. Like For example, playing video games is always associated with men. Whereas women also do play video games. So it is a stereotype that men play video games. Similarly, beauty saloons are always stereotyped with women. Whereas men do go to saloons.
So such type of perception is called Stereotyping.