Albert Einstein's cosmological constant was proved wrong by Hubble as he proved the universe is expanding so it doesn't need a constant to stop it imploding.

The Earth is not 12 billion years old. It is more like 5 billion years old.

Hubble's constant cannot be determined from the age of the Earth.

Hubble's constant describes how fast the universe is expanding. It can be determined by looking at the redshifts of stars that are a known distance away. From the redshift, one can determine the velocity of the star. Then Hubble's constant is defined as follows: v=Hd where v is the velocity of the star, H is Hubble's constant and d is the distance to the star. The current accepted value of Hubble's constant is about 71 km/s/Mpc.

h=vd

I can't find the answer anywhere. Everywhere I look it just says that it's still not the exact value of the Hubble constant. Why?

Hubble was an astrophysicist in the early 20th century. He helped discover the rate at which the universe is expanding, which is now given by the Hubble constant. (H0=69km s^-1 Mpc^-1)