3 weeks 6days old and sleeping 5 hours at night

Hi guys.  My LO sometimes sleeps about 5 hours at the time at night and he is only 3 weeks 6 days old.  Is that normal? Should I wake him up before it gets to 5 hours between feedings or let him sleep. He would wake up if he is hungry. Please let me know. All of the supposed "professional " advice don't let them go more then 4 hours at night between feedings is that true?