input: Write a python function to group employees by their age and calculate the average age for each group.
  assert group_employees_by_age([{"name": "Alice", "age": 25}, {"name": "Bob", "age": 25}, {"name": "Charlie", "age": 30}]) == {25: 25, 30: 30}
  assert group_employees_by_age([{"name": "David", "age": 40}, {"name": "Eve", "age": 40}, {"name": "Frank", "age": 40}]) == {40: 40}
  assert group_employees_by_age([{"name": "Grace", "age": 35}, {"name": "Heidi", "age": 35}, {"name": "Ivan", "age": 45}]) == {35: 35, 45: 45}
output: def group_employees_by_age(employees):
      from collections import defaultdict
      
      age_groups = defaultdict(list)
      
      for employee in employees:
          age_groups[employee['age']].append(employee['age'])
      
      avg_ages = {age: sum(ages) // len(ages) for age, ages in age_groups.items()}
      
      return avg_ages