Question: how old was djokovic when he started playing tennis
[{'answer': 'four', 'provenance': [{'wikipedia_id': '16100029', 'title': 'Novak Djokovic', 'start_paragraph_id': 2, 'start_character': 478, 'end_paragraph_id': 2, 'end_character': 482, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}, {'provenance': [{'wikipedia_id': '16100029', 'title': 'Novak Djokovic', 'start_paragraph_id': 8, 'start_character': 0, 'end_paragraph_id': 8, 'end_character': 329, 'bleu_score': 0.9657992495762461, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 1169513956551468873}, 'section': 'Section::::Early and personal life.\n'}]}]