Red dwarfs make up about 75% of the stars in the Milky Way, and a red dwarf with about a third of the Sun’s mass can burn for up to about 14 trillion years. That is more than 1,000 times the current age of the universe (13.8 billion years) and far beyond the Sun’s 10-billion-year lifespan.
The reason is fuel use. A red dwarf is cool and dim, so it burns hydrogen very slowly. Its interior churns, carrying helium made in the core outward while fresh hydrogen sinks inward, so the star can use nearly all of its hydrogen instead of just the core’s share. No red dwarf has died of old age yet because the universe is too young. Proxima Centauri, the nearest star to the Sun, is one. It is too dim to see without a telescope.
~14 trillion years
Longest red dwarf lifespan