Why my systolic blood pressure is high its in sometime 145 or 140 but diastolic is always in 70s my age 21 height : 5.9 weight : 85 kg no other health issue?

Can't say: High systolic pressures are still hypertension & the cause can be elusive. A basic workup by your doc may find an answer. Many times no answer is found & the process will be labeled "essential" hypertension meaning we don't know why. Diet & lifestyle change may help some but meds may eventually be needed. Long term damage can occur without obvious symptoms.