How often does 28 yr olds have a stroke? and what would cause it?

Very rarely ....: Age is the single most important risk factor for stroke, but most of it is at ages older than 55. Stroke in a person younger than age 45 is less than 1/1,000. It could be caused by the usual: high blood pressure, smoking, high cholesterol, diabetes, but other causes from a cerebral hemorrhage/aneurysm or a blood vessel dissection (rupture) could be a cause. Control risk factors mentioned above.