The causes of blood pressure has been divided into two categories namely primary hypertension and secondary hypertension.
There is no identifiable cause in primary hypertension. This type is known to develop gradually,year by year.
Secondary hypertension is usually caused by an underlying condition. There could be a bunch of reasons for that like kidney problems,thyroid problems. It could also be due to certain pills that affect your system like birth control pills,some prescription drugs and maybe due to some illegal drugs like cocaine etc. Factors like one's declining age could be a reason as it's common for people to get this who are in their 60s. There are also reasons like race,family history and lineage. Also health issues like being too overweight or obese or not indulging in physical activity,etc could play major roles.