Blood clots, when they are small and only occasional, is common and normal on heavy flow volume days. If blood clots are big (larger than quarter) and occur frequently then there might be any underlying medical conditions such as fibriods, endometriosis, adenomyosis, perimenopasue, menopause, stress, weight gain and blood dyscrasias.
Periods can get delayed by any number of days, from 30 days to 6 weeks. If next cycle starts from 28 +/- 7 days from the first date of last menstrual cycle then it is considered a normal cycle. Any delay more than it is considered abnormal.
Having a lot of dairy products is not the best idea, as it can cause cramping. Dairy products like milk, cheese, and ice cream contain arachidonic acid (an omega-6 fatty acid), which can increase inflammation and can intensify your period pain.
Do some life style modifications such as practicing yoga, maintaining healthy weight , exercise regularly , use more ginger and cinnamon , get daily dose of vitamins. If you miss 1 or 2 consecutive cycles then please consult a doctor to get evaluated.
It is typical sign of old blood or blood that has taken longer to leave
It may not be same for each person but usually it is any age from between 40's to 60's years.