Is 16 days considered a late period?

No, generally 30 days is late. A late period can be caused by stress, sickness, too much dieting, and pregnancy. Not all periods are 28 days and can go as long as 35 day between periods. . If you are young and just starting your period it will take a year or so before it becomes regular. The same thing happens with menopause the periods become irregular because of hormones.