How variable is human flexibility?

Do we all have a base flexibility, or is it just that "naturally more flexible" people do more workouts and perform more motions that require flexibility?

If I gain flexibility, then stop stretching, will I lose it as quickly as I gained it. Is my upper limit drastically different from somebody else's?

I can never remember being able to touch my toes, do I ever have a chance of putting my hands flat on the floor with straight knees?