Complex sentence: He went to school in Lviv (Polish: "Lwów"), and wrote his first poems at the age of 14, whose would be published two year later in the newspaper "Słowo Polskie", where he soon became a theatre critic.
Split into simpler sentences: He went to school in Lviv (Polish: "Lwów"), and wrote his first poems at the age of 14. These were published two years later in the newspaper "Słowo Polskie", in which he soon became a theatre critic.