对于一组给定的客户数据，编写Python脚本以生成一个简单的汇总报告。


客户数据：
姓名,年龄,邮箱地址,购买记录
John Doe,30,john.doe@email.com,3
Jane Smith,25,jane.smith@email.com,5
Bob Johnson,42,bob.johnson@email.com,2
```
data = [['John Doe', 30, 'john.doe@email.com', 3],
        ['Jane Smith', 25, 'jane.smith@email.com', 5],
        ['Bob Johnson', 42, 'bob.johnson@email.com', 2]]

# calculate total number of customers
num_customers = len(data)

# calculate average age
total_age = sum([row[1] for row in data])
avg_age = total_age / num_customers

# calculate total number of purchases
total_purchases = sum([row[3] for row in data])

# print summary report
print(f"Number of customers: {num_customers}")
print(f"Average age: {avg_age}")
print(f"Total number of purchases: {total_purchases}")
```

输出：
```
Number of customers: 3
Average age: 32.333333333333336
Total number of purchases: 10
```