My nephew was diagnosed with centro-parietal epilepsy and i would like to know what it is, how often it is diagnosed, and if he (15 months old) can grow out of it. also if there are any complications that can occur?

Your best source of information on any such condition are the people involved in the diagnosis and treatment plan. Centro-parietal is just a region of the brain giving rise to the seizures. It is not a valid separate diagnosis. Many childhood epilepsies fade as they get older, some persist well into adulthood. The therapy uses med trials to find one or more that works, with follow-up for years.