Like all the planets, Venus formed approximately 4.6 billion years ago when the Sun and the Solar System came out of the solar nebula. So, the age of Venus is 4.6 billion years old.
Before the Solar System, there was just a large cloud of hydrogen gas in a giant nebula. Some event, like a nearby supernova explosion put a shock into the cloud, and caused it to begin collapsing. Many stars, large and small, formed in this nebula, and one of these went on to be the Sun. As the material condensed together, conservation of momentum caused it to spin up and flatten out.
A protoplanetary disk of material formed around the newborn Sun, and it was here that the planets formed. Dust clumped together to form rocks, rocks smashed together into boulders, and mountain-sized objects became protoplanets. In the first few hundred million years of the age of Venus, it’s likely that the planet was smashed many times by these large asteroid and protoplanets. But eventually, Venus became the dominant object in the region, sucking in everything with its gravity.
We know that Venus was probably the victim of a large collision because it rotates in the opposite direction from the rest of the planets in the Solar System. A large collision could have turned its rotation backwards.
How do we know Venus’ age? We can’t measure the age of Venus directly, because of the intense heat and pressure on the surface of Venus. Instead, scientists measure the age of meteorites that have fallen to Earth. After analyzing hundreds of objects, scientists have found that they all formed at approximately the same time. These meteorites are the leftover pieces from the formation of the Solar System, and help prove that all the objects in the Solar System formed at the same time.
And so we know that the age of Venus is 4.6 billion years old.
We have also recorded a whole episode of Astronomy Cast that’s just about planet Venus. Listen to it here, Episode 50: Venus.
NASA Solar System’s Big Bang