What is the estimated main sequence lifespan for Red Dwarf (M-type) stars?

Trillions of years

Red dwarfs, classified as M-type stars, represent the opposite extreme of the stellar longevity spectrum from the O-type giants. These low-mass objects possess significantly lower core temperatures and exert far less gravitational pressure than larger stars. Consequently, they consume their supply of hydrogen fuel at an exceptionally slow, or glacial, pace. Because their fuel consumption rate is so minimal, their predicted main sequence lifespans stretch out into timescales measured in the trillions of years. Since the universe itself is estimated to be only about 13.8 billion years old, no red dwarf that has ever formed is near the end of its existence; they are the longest-lived objects known.