Complex sentence: During his puberty and incipient adolescence, he was a literary prodigy; began to write relentlessly at the age of only 14, opening in that way what should later become the first of his two creating phases.
Split into simpler sentences: During his puberty and incipient adolescence, he was a literary prodigy. Pasos began to write relentlessly at the age of 14, opening in that way what should later become the first of his two creating phases.