input: Write a function to calculate the average age of a group of people.
  assert calculate_average_age([("Alice", "30"), ("Bob", "25"), ("Charlie", "35")]) == 30.0
  assert calculate_average_age([("Eve", "45"), ("Frank", "55")]) == 50.0
  assert calculate_average_age([("Grace", "20"), ("Heidi", "40"), ("Ivan", "60")]) == 40.0
output: def calculate_average_age(people):
      total_age = sum(int(age) for name, age in people)
      return total_age / len(people)