The BBT is the best theory we have of how the universe appears to have come into the state we see it in right now. It is described as an expansion, as opposed to an explosion. The galaxies, solar systems, stars and planets that we can see and measure, are a result of a very long process - part of which has the gravity component which helped shape planets into spheres - from my understanding.
Anyway, the objects within our solar system are of different ages, so we can say that some planets, stars, galaxies, etc., are older or younger than others. Every object was not created simultaneously.
Are you excited about the exoplanets? I know I am!