Sorry Mike you do not make sense at all. The figure above measures the high blood pressure and the figure below measures the low blood pressure.
You cannot calculate what the correct blood pressure should be if you deduct the low pressure from the high pressure reading and if the resulting figure happens to be the person's age then that is the correct blood pressure for that person.
This is not how it works at all, it is quite possible for a 45 year old to have exactly the same blood pressure (high and low) as a 65 year old has. It depends on many factors, age is certainly one. My other half is a 5 years younger than me but has both high/low levels higher than mine.
Hope that makes some sense.