Stars are generally between 1 billion and 10 billion years old. Some stars may even be as old as 13.8 billion, having formed around the time of the observed universe. The sun is the nearest star to Earth, with the star Proxima Centauri being the next closest, roughly 4.2 light years away. It would take a craft 75,000 years to reach that point.
Extremely dense stars that have gone supernova can actually form into a black hole. Other supernova leave behind white neutron stars that are about 25 miles in diameter and have heavy cores made of neutrons. Stars do not twinkle. Rather, they appear that way due to the Earth's atmospheric turbulence that deflects the light that reaches human eyes.
Stars vary in color according to their temperature. From highest to coolest temperature, the stars' colors are blue, white, yellow, orange and red. Brown stars are the lowest temperature. Since it takes the light from stars millions of years to reach Earth, the stars observed in the sky are actually from back in time. There are about 200 to 400 billion stars in the Earth's Milky Way Galaxy alone.
As a star nears the end of its life, it transforms helium into the heavier elements of carbon and oxygen. It also changes its density, color, mass and size at this time.