input: Write a python function to return the average age of students in a given dictionary.
  assert average_age({'John': 18, 'Maria': 20, 'Alex': 24}) == 20.67
  assert average_age({'Alice': 22, 'Bob': 24, 'Charlie': 26}) == 24.0
  assert average_age({'Tom': 30, 'Jerry': 28}) == 29.0
output: def average_age(students):
      total_age = sum(students.values())
      number_of_students = len(students)
      average = total_age / number_of_students
      return round(average, 2)