def convert_age_units(age_unit):
    """
    Simple function to convert proband age units to cgap standard

    Args:
        age_unit (str): proband age unit

    Return:
        str: cgap age unit
    """
    convert_dict = {
        "d": "day",
        "w": "week",
        "m": "month",
        "y": "year"
    }
    return convert_dict[age_unit.lower()]