Complex sentence: He had his first seizure at the age of 16, and at the age of 25, he underwent a two-stage resection of the corpus callosum for relief of intractable epilepsy.
Split into simpler sentences: He had his first seizure at the age of 16. At the age of 25, he underwent a two-stage resection of the corpus callosum for relief of intractable epilepsy.