Question

Given that our solar system is now about 4.6 billion years old, when will we need to worry about the sun running out of hydrogen for fusion?

Answer 1

The approximate lifetime of a star like our Sun is in the range of 10.3 billion years. At a current age of 4.6 billion years, this will leave (10.3 - 4.6) or approximately 5.7 billion years before the supply of hydrogen fuel (and thereby, helium) will run out.