The highest blood pressure known so far that a human can have which is not good is a blood pressure reading of 240 over 200 which is very dangerously high.
You never want your blood pressure reading to get that high as it can be deadly.
When your blood pressure reading is 120 over 80 then it's in the normal range but if it goes higher it's getting into the prehypertension range and if your blood pressure climbs above 140 Systolic then you need to seek medical attention.
You can help to lower your blood pressure naturally by avoiding stress, getting plenty of sleep, and taking a tablespoon of apple cider vinegar once or twice per day or you can also mix Apple Cider Vinegar with a glass of warm water, lemon juice, and honey and drink a couple glasses of the Apple Cider Vinegar mixture during the day.
Also try taking a 15 to 20 minute walk everyday as walking is a good way to keep your blood pressure to the normal levels and helps to boost your heart health and other health.
Walking everyday has shown to increase a persons lifespan as well.