Any advice that ends with "at his age" or "your age" is BS. There is no distinction between "his age" and "your age" or any other "age". The body was designed to function the same no matter what age it is.
There is a reason that older people develop health problems as often as they do, and if you'll look around and notice, you'd see younger people now developing the same problems.
The reason is, people don't drink enough water.
After the age of 20, we all start losing our perception of thirst. It gradually diminishes until, by the time we reach our advanced years, it's hardly noticeable at all. And thus, because we've been taught that thirst is a reliable indicator of when to drink water, as we drink less water we develop health issues more often - like high blood pressure.
Thirst should never be relied on as a sign that we need to drink water. The average adult loses around 2 quarts of water per day through normal body functions but doesn't replace it properly. So they maintain a dehydrated state. Water regulates all of the functions in the body, so when a perpetual water shortage exists it affects those functions.
Younger people don't have a problem with thirst perception, but they do gravitate to soft drinks, which do not supply the body with the water it needs, This creates a dehydrated environment in them as well, and their bodies react accordingly.
Everyone's blood pressure, no matter the age should be around 120/80. This doesn't mean that your dad is in any kind of danger. It just means that he needs to increase his water intake.
Nothing serious - but maintaining proper hydration will help prevent other issues besides the blood pressure such as cholesterol levels - another common problem experienced by older people.