I am over 40 years old, but since the last two months I have been having my period late?

Many possibilities. Reasons for missed /late periods: low body weight, obesity, marked weight gain or loss, over-exercise such as in endurance athletes, breast-feeding, stress, illness, eating disorders (bulimia or anorexia), travel, hormone irregularities, drug use, medications (i.e., birth control) or med problem (polycystic ovary syndrome or Asherman’s syndrome. #1 reason is pregnancy.
? menopause. We age and the cycle changes, and then menses stop...Very variable collection of symptoms and signs... See a doctor and check it out.