Hummmm......it is hard to even make a guess without any pics. Do you know the breeder/lineage?

That being said, most Pastels do tend to darken with age ( mine certainly has ). The few exceptions to this being selectively ( meaning more expensive ) bread lines such as the Lemons, Grazini's and a few various crosses of the before mentioned. It is typical for most but not all Ball Pythons to darken as they mature into adult hood.

The only pythons I am aware of getting brighter with age are the Morelia's, but there are probably others that I'm not aware of as of yet.

If I am out of line or off base on this, I'm sure someone will respond with additional input. Hope this helps