如何根据Python中的条件合并两行pandas数据帧？

import pandas as pd

data = {'Name': ['Tom', 'Nick', 'John', 'Alex'],
        'Age': [20, 25, 30, 35],
        'City': ['New York', 'Paris', 'London', 'Berlin']}
df = pd.DataFrame(data)

   Name  Age      City
0   Tom   20  New York
1  Nick   25     Paris
2  John   30    London
3  Alex   35    Berlin

condition = df['Age'] < 30

merged_df = df[condition].groupby('City').agg({'Name': ' '.join, 'Age': 'sum'}).reset_index()

       City   Name  Age
0    Berlin   Alex   35
1    London   John   30
2  New York  Tom    20