The universe is very very very very very big.
Therefore it is very very very very very old.
We know this because of light, which travels at a constant rate of 186,000 miles per second. Using a method called triangulation (using geometry and trigonometry) we can calculate the distance between us and objects in space. This reveals distances so great that we can scarcely comprehend them, distances so great that we must measure them in light years.
The distance which light travels in one year is 5,878,630,000,000 miles.
The nearest star to us is over 4 light years away.
The most distant objects we can observe are nearly 13 billion light years away.
Because of this we know that the universe is at least 13 billion years old.
The age of the earth and our solar system are also well understood and have been independently verified using many different methods.
Rocks from asteroids, mars, the moon and earth all agree upon an age of around 4.6 billion years.
Because of the Hubble space telescope we can actually OBSERVE the formation of solar systems. We see from the birth of stars as gravity causes compressed gas to collapse in on itself starting nuclear fusion…
…to the formation of planets.
These are things that we can actually SEE directly.
Why then after knowing this, would we assume that our Earth and our solar system are any different?