Complex sentence: At the age of 39 years old, Renzi overcame Benito Mussolini as the youngest person ever to become Prime Minister of Italy since unification in 1861; moreover he is the first to lead a government serving as a Mayor instead of a Member of Parliament.
Split into simpler sentences: At the age of 39, Renzi overtook Benito Mussolini's record as the youngest person to become Prime Minister of Italy since unification in 1861. He is also the first to lead a government serving as a Mayor instead of a Member of Parliament.