return list dictionary of the three biggest numbers in a list of dictionaries

test_data = [{'name': 'Bob', 'age': 25},
             {'name': 'Tom', 'age': 18},
             {'name': 'Sally', 'age': 39},
             {'name': 'Jane', 'age': 45},
             {'name': 'Dorothy', 'age': 20}]

test_data.sort(key=lambda x: x['age'], reverse=True)

print(test_data[0:3])