We used to start treating high blood pressure (hypertension) when it is consistently above 140/90, in order to prevent stroke and heart attack. Unless there is another risk factor such as high blood sugar and high cholesterol, or a family history of heart disease and stroke, usually borderline high blood pressure around 140/90 does not need medication. The best treatment for borderline hypertension or pre-hypertension is lifestyle changes, such as exercise, low salt diet (no more than 1500mg sodium) a day, 5-10 lb weight loss, stop smoking and drinking alcohol, etc. There is new evidence for those over 60 years of age who do not need medication treatment until the blood pressure is consistently 150/90.
The newest hypertension guideline is published in 2014, JN8 (Eighth Joint National Committee) a panel of physician and scientist analysing at what blood pressure without medication treatment would correlate higher death rate (mortality) from heart and kidney disease, or more hospitalization for heart attack, stroke, dialysis, surgery for revascularization (like cardiac stent). They found that for people over 60 yo, the medication should be started after 150/90. For those who are under 60, the threshold to start medication treatment is 140/90.