As I got older and realized that others didn't see the deceased people like I did I began to ignore them. As I ignored them they faded from my sight. I think they did this as a kindness.
Some people are older when they discover for the first time that they can interact with the deceased. They generally were sensitive and had unusual experiences as a child, such as knowing about the upcoming death of someone around them or knowing someone had passed before it is announced. However, Mediumship is the act of bridging the physical world and the world of spirit by conscious active communication. Not all who are sensitive to the other side will develop into mediums, though many do.
Mediums are people that consciously communicate with the deceased, on demand and consistently, anytime they wish. Being a natural born medium means that you know about the spirit world, they know about your ability to communicate with them, and thus there can be a dialogue of sorts between the two of you on demand.