Question: when did the voting age change from 21 to 18
[{'answer': '1970s', 'provenance': [{'wikipedia_id': '630522', 'title': 'Voting age', 'start_paragraph_id': 2, 'start_character': 118, 'end_paragraph_id': 2, 'end_character': 123, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}, {'provenance': [{'wikipedia_id': '630522', 'title': 'Voting age', 'start_paragraph_id': 2, 'start_character': 0, 'end_paragraph_id': 2, 'end_character': 265, 'bleu_score': 0.910036530027129, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 4483080766977121570}, 'section': 'Section::::Abstract.'}]}]