You mean "What is the sun's age"?

"Sun has a age to see how much hydrogen it has converted over its life versus how much is left for the future". 

Present age:- 4.6 billion years

At some 4.6 billion years old, the Sun is about halfway through its life. In another 5 billion years it will be a normal “adult” star no more. Here’s the skinny on the upcoming demise of the star that you owe everything to: light, warmth, energy, and life.

How we know the sun's age:

How do we know how old it is? We look at the age of the whole solar system, because it all came together around the same time.

To get this number, we look for the oldest things we can find. Moon rocks work well for this. When astronauts brought them back for scientists to study them, they were able to find out how old they are.

The Predicted age of the sun, after which it will convert into a white dwarf, is somewhere around 10 billion years, so, kinda like 5.5 Billion years left. I left the White Dwarf phase out, and am considering the sun’s death when it stops being a red giant, although, that does not happen, as the Sun, as a white dwarf will shine, although, much dimmer than it does now. I considered the death as the ending of the red giant phase, as the white dwarf phase is rather, long. Somewhere around 100 billion years, if my memory serves me right. That, is longer than the current age of the universe.

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Manomay Shravage
No I meant why does it age
Sangeetha Pulapaka
Because the Sun continues to 'burn' hydrogen into helium in its core, the core slowly collapses and heats up, causing the outer layers of the Sun to grow larger. So, as time passes the sun gets larger. This has been going on since soon after the Sun was formed 4.5 billion years ago. It is a very gradual process, and in the last 4 billion years, the Sun has barely grown by perhaps 20 percent at most. It will not grow by much more than another factor of a few for the next 6 billion years, but at that distant time, it will make a rapid transition to a red giant phase and its outer surface will expand by several hundred times to perhaps the orbit of Venus. So, we have to say that the sun like a human can age too, but ages much much much slower. Thank god for that!