def file_age(file_path):
    """
    Returns the age of a file in seconds since its last modified timestamp.

    :param file_path: str: The path to the file.
    :return: float: The age of the file in seconds.
    """
    if not os.path.isfile(file_path):
        return 3600 * 24 * 1000.0

    # Get the current time and the file's last modification time
    current_time = time.time()
    file_mtime = os.path.getmtime(file_path)

    # Calculate the file age in seconds
    file_age_seconds = current_time - file_mtime

    return file_age_seconds

    Returns the age of a file in seconds since its last modified timestamp.

    :param file_path: str: The path to the file.
    :return: float: The age of the file in seconds.
    
python/aitemplate/utils/io.py