def replace_age_range_label(header):
    """
    The CSV files contain a field called AgeRange,
    but we split the range into two separate fields when storing in the DB
    :param header: The list of fields at the top of the CSV file
    :return: The index of the AgeRangeStart field
    """
    index = header.index('AgeRange')
    header[index] = 'AgeRangeStart'
    header.insert(index + 1, 'AgeRangeEnd')
    return index