Complex sentence: Three months younger than Putin, Ivanov had been a student contemporary of Putin's in their hometown of Leningrad where both completed competitive specialized secondary education programs (Putin in chemistry, Ivanov in English language) before attending Leningrad State University.
Split into simpler sentences: Three months younger than Putin, Ivanov had been a student contemporary of Putin's in their hometown of Leningrad. Both completed competitive specialized secondary education programs (Putin in chemistry, Ivanov in English language) in Leningrad before attending Leningrad State University.