I have heard many perspectives on sleep patterns and I was wondering...... In regards to night owls and eary birds.... have they proven it to be a biological/chemical sleeping pattern in the body to prefer the night life or early morning? Or, is it just a lifestyle choice that can change if you choose to?

My two sons are night owls, and one of them has to be in training this week from 9 am to 5 pm. He prefers night shifts and stays up into early morning, prefering to sleep until midday. Could it be a sleep cycle pattern related to his age also? He is 22 soon, and the other son will be 19. I am 47, and prefer to bed early and up early in the morning. Does it change with age?