How old is the sun and how can scientists calculate it?

Our sun is 45 billion years old, that is, 4.5 billion years old, but how can we know its age, and can we know almost the time when its radiance will turn off, this is what scientists answered.
According to the "spaceplace.nasa" site, scientists looked at the entire solar system age, because it all met around the same time, and to get this number they search for the oldest things they can find and estimate their age, such as the moon rocks that astronauts returned to scientists for their study , And were able to find out how old they are.

How long will the sun shine?
If the sun is four and a half billion years old, how long will it continue to shine. Stars like our sun are burning for about nine or ten billion years.
The answer to this question came from the fact that our sun is about halfway through its life, and it still has about 5,000,000,000 years, or another five billion years.
And with the end of life expectancy, the sun will become a red giant, that is, it will get bigger and cooler at the same time, and when that happens, it will be different from the sun that we know today, and more surprisingly, it will become about 100 times brighter than it is now but without heat.
 
Is the Sun 45E+9 years old or 4.5E+9 years old? Telescope observations of the Sun since the time of Galileo do not *date* or show the *age* of the Sun. Clair Patterson in mid-50s used radiometric dating of meteorites to develop a model to calculate the age of the solar system and by circular argument, the age of the Sun. Once the meteorite age paradigm fixed this age, the Sun was modeled to plot accordingly on the H-R star diagram for its age. A direct age measurement for the Sun does not exist.