What causes only the systolic to be high between 130-145 and diastolic normal in a young adult? no medical conditions and healthy in general

B/P is a measure of: the force of blood on blood vessels as it flows thru arteries. Systolic is the force when the heart is actively pushing blood into the arteries. Diastolic is the left over force when the heart is at rest. Exercise, stress & anxiety can increase systolic B/P. Stiff or tight blood vessels & increased volume of blood can increase both systolic & diastolic B/P. B/P should be measured at rest!

Most likely: essential hypertension. and exercise. You should take your BP 2-3 times daily at home. These readings should average 120/80 at your age. If your BP is high, initial treatment is life style modification, including weight loss, low sodium diet. If this does not work, there are many effective medications with few side effects.