Veins have nothing to do with your blood pressure. When measuring the blood pressure, the arterial pressure (pressure in your arteries) is measured. In your veins, your blood pressure is far lower, usually 0-20 mmHg.
When you take a warm shower, your blood vessels will dilate, which increases venous circulation, and as the temperature increases, blood vessels will pop out closer to your skin as a part of the natural temperature control mechanism, making the veins more visible.
At age 24, permanent hypertension is very uncommon.
Your veins are not new. They can't just appear out of nothing. But from time to time, they can be far more visible.
If you are concerned about your blood pressure, stop smoking. Smoking also contribute to increase the SVT events.
Have you figured this out ? I have a very similar situation