A normal optimal blood pressure level is 120/80mmHg or lower, and high blood pressure is 140/90 mmHg or higher, no matter what your age is.
If your blood pressure gets to 140/90 mm Hg or higher you need to lower the blood pressure and may have to seek medical attention if it doesn't lower.
When your blood pressure is getting into the 180/120 or higher then you're at risk for a stroke although even a lower blood pressure that's still high can cause a stroke so it's important to get medical attention and get that blood pressure lowered back to normal.
Having high blood pressure increases your risk for stroke, heart disease and heart attacks.