Complex sentence: Abdul Ilah stepped down in 1953, when Faisal came of age, but he continued to be a close adviser of the young king, and an advocate of a pro-Western foreign policy.
Split into simpler sentences: Abdul Ilah stepped down in 1953, when Faisal II came of age. But he continued to be a close adviser of the young king, and an advocate of a pro-Western foreign policy.