What is high BP? A level of blood pressure that has been proven to shorten ones life and a level of BP that if treated prolongs ones life. The best is to be below120/80. However for treatment we use 135/85 at home as high. At your age above 135/85 at home would be consider HTN that needs to be lowered. Always try DASH diet first.
Symptomless disease. High blood pressure (BP) is a disease where the pressure in your arteries is too high, where the systolic is >140 or the diastolic is >90 (see my colleague's answer for an explanation of systolic and diastolic.) ideally the BP should be <130/80. High BP often is without symptoms but needs treatment to prevent heart disease & stroke. Untreated high BP can also lead to kidney disease and impotence.
See below. The pressure inside the arteries is too high. The systolic pressure is that when the heart contracts and the diastolic is the pressure when the heart relaxes. It is most commonly measured with a blood pressure cuff which is an indirect measurement. Sometimes a needle is place within an artery and attached to a transducer to measure the pressure directly and continuously in sick patients.