I once discovered in a now past role that a junior employee made significantly more than me, as a senior employee. I had about 12 years experience and was hired for this expertise and experience, very quickly by this company for a role they were trying to fill for several months. The salary was good, one that was a bit more than my last. I then found a form that showed a junior employee, 1 year out of college, made 15k more than me. 

My question might be how to explain this? It's in the development field. Let's assume he had some advanced skill they were seeking. Does that justify what might be twice an average salary for 1 year experience? Is it a matter of better negotiating for him, or poor negotiating for me perhaps? I feel like all this might get him a high junior salary, but this totally surprised me.