I'm still a new programmer (about 6 months of practice), so I was actually thinking about trying to make a PC implementation of a card game I've already prototyped.

Would that be allowed?  Or is that considered an "existing asset", and I should think about trying something else?

The game has to be created from scratch. You can use stuff like free extensions, libraries, code snippets and such, but you can't use an existing game base like your card prototype.

Have fun!