def slice_age_df(df, col_nms):
    """Slices a dataframe according to the list of column names provided.

    Args:
        df (pd.DataFrame): DataFrame to be sliced
        col_nms (list of str): column names as string in a list

    Returns:
        pd.DataFrame: A dataframe sliced down to only the columns required."""
    age_df = df.loc[:, col_nms]
    return age_df