The reason I believe in OLD earth creationism is because I believe that God created the world, but I still accept scientific evidence that the universe, and therefore our earth is millions of years old. While I respect the beliefs of YECers, I think that the scientific evidence proves beyond a doubt that the universe and therefore the earth and our solar system is older than 6000 years.
My belief in OEC is based in the science of astronomy.
Cases in point - the crab nebula and the veil nebula.
Check out these websites
http://www.seds.org/messier/m/m001.html
and
http://www.astropix.com/HTML/E_SUM_N/VEIL.HTM
The explosion of the star that resulted in the crab nebula was first observed in the year 1054 A.D. Now, if we accept the YEC position that the earth is only 6000 years old, then why do we see remnants of stars that have exploded, if they hadn't been created millions if not billions of years ago (at least in the way we as humans measure time)? The lifespan of a star is millions of years, even billions of years, depending on how massive it is. If you study the process of nuclear fusion within the core of a star, we know that it's going to take a long time for the star to burn it's supply of hydrogen, then helium, and so on through the process of fusing heavier and heavier elements. Our own sun, once it exhausts its supply of hydrogen will start burning helium, at which point it'll turn into a red giant. More massive stars can form heavier and heavier elements. This means that the star must have been formed millions if not billions of years ago. Therefore, in my mind, it stands to reason that our sun, and therefore our solar system, is no exception. This is basic material in any astronomy class.
To me, there are questions that YEC doesn't answer in a very satisfactory manner in my opinion -
1. How do you explain nebulas in YEC?
2. How do you explain black holes in YEC?
3. How do you explain pulsars in YEC?
I've read the material on answersingenesis.com, but in my mind, it's bad science at best. One of my favorite books on the cosmos and the creation of the universe and the earth is Hugh Ross'
The Creator and the Cosmos.