Is hypertension preventable?

Yes and no..... Everyone can do his/her part to prevent or reduce the severity of high blood pressure. To do this, follow a health diet (dash is excellent - look it up), exercise daily, maintain a healthy weight and don't eat out too much (salty). Some people, however, have hypertension despite lifestyle: they will usually need medicine. The amount needed, can be reduce with keeping the healthy life as above.
Perhaps. Hypertension is blood pressure to a certain predefined level. There are many causes. Lifestyle is a major one. Being on a dash diet helps. Keeping weight at optimum helps. Avoiding too much alcohol, getting plenty of rest and elimination stress helps. Some people develop hypertension with aging and for other reasons that are just not preventable. Discuss this with your pcp.