How long can a star shine?

Answer 1

Small dim stars can shine for a trillion years or more. The more massive a star is, the BRIGHTER it is, and the faster it burns out.

Our Sun is perhaps just a bit larger than average, but not by a whole lot; our Sun has already burned for 4.5 billion years or so, and we can expect as much more. But it won't be the Sun as we know it; in 3 billion years or a little more, it will expand into a red giant.

Very large stars like Betelgeuse are already quite old and about to die - spectacularly! - at fairly early ages. (Some time within the next 100,000 years) And yet, Betelgeuse is only about 100 million years old!