I think part of this is normal coping humor.

A young person can feel conflicted between feelings of (a) relief that they are not in an endangered demographic, and (b) anxiety for people who are endangered and remaining self concern as they do not truly feel safe.

Oversimplifying the situation with humor (only older people need to worry, I am not old) temporarily releases some anxiety.

Dark humor does not necessarily reflect dark motives or values.

Taken too far it can become callous denial, also likely as a anxiety numbing strategy.

But most people just need a break from worry in a way that doesn’t harm anyone.