Complex sentence: De Gaulle won a place at St Cyr in 1909; his grading was mediocre (119th out of 221 entrants) but he was relatively young and this was his first attempt at the exam.
Split into simpler sentences: De Gaulle won a place at St Cyr in 1909. His class ranking was mediocre (119th out of 221 entrants), but he was relatively young and this was his first attempt at the exam.