hypertension normal tension ranges according to age and consequences

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I am in my 20's and occasionnally my blood pressure goes over 170, is there any bad consequences that? or does it happen to people regularly. otherwise my blood pressure is usually fine.
Any causes of it? It can happen even when I'm not doing anything, and my salt intake is not that high
I never had this condition before so I don't know very much about it.
thanks for you help!