Question: when did the age to vote changed to 18
[{'answer': '1971', 'provenance': [{'wikipedia_id': '630522', 'title': 'Voting age', 'start_paragraph_id': 5, 'start_character': 441, 'end_paragraph_id': 5, 'end_character': 445, 'bleu_score': 1.0, 'section': 'Section::::History.\n'}]}, {'provenance': [{'wikipedia_id': '630522', 'title': 'Voting age', 'start_paragraph_id': 56, 'start_character': 0, 'end_paragraph_id': 56, 'end_character': 959, 'bleu_score': 0.8550528353030921, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 11837672151030392064}, 'section': 'Section::::Debate on lowering the voting age to 16.:United States.\n'}]}]