Bev likes to be up late at night and sleep in; caleb likes to wake up with the sun and go to bed early. a psychologist would say they have different

Based on the description,  a psychologist would say they have different chronotypes
chronotypes is a circadian rhytm inside ourbody that affected our body's sensitivity of sunlight.
For some people, exposure to sunlight makes them feel energized and ready for their activities, which make them prefer to go early.
On the other hand, exposure to sunlight put some people into a resting mode, which make them prefer to be a night owl,

Ithink the answer is baby boomers ?

What was the length to begin with?