Q1 what is a life Span ? Life span defines the existence of anything that how long an object or living thing take to reach its end point and after reaching the its end point , it will disappear from the universe.
Q2 what is life span of star ? It is the time star existed in the universe. After this time the star got disappeared from the universe. Q3 What is the age of the star ? MY ASSUMPTION $= According to my science age of the star depends upon the speed of time on it. If the speed of time on any star is fast then the the age of star will be lesser than the comparison of star where the speed of time is slow. The speed of time at any point depends upon the Gravity of that point.The point having low gravity have time speed fast but, where the gravity is high the time speed becomes slow. So, the points having high gravitational field have large life span. Q BUT, ON WHAT THE GRAVITATIONAL FIELD DEPENDS ? The gravitational is directly depends upon the mass of object.Means the point having high gravitational field have the high field of gravitational. And, the lower in mass of any object will reduce its gravity. FOR INSTANCE , its a fact that the life span of our earth is lesser than the sun , and the surviving period of moon is lesser then earth . And, if you check the mass pf the sun is million time more than the earth , same phenomenon in case of earth and moon. SO, i can say that the life span of any object depends upon its mass.
This is picture of dying star.