My row lists:

```
List rowlist = [Student(name: 'John',age: 12),
             Student(name: 'Kity',age: 13),
             Student(name: 'Micle',age: 14),
             Student(name: 'Jack',age: 12),
             Student(name: 'Cha',age: 13),
             Student(name: 'Duc',age: 13),
             Student(name: 'Ran',age: 12)]

```

Expected result:

```
List result = [
               [
                Student(name: 'John',age: 12),
                Student(name: 'Jack',age: 12),
                Student(name: 'Ran',age: 12),
               ],
               [
                Student(name: 'Kity',age: 13),
                Student(name: 'Cha',age: 13),
                Student(name: 'Duc',age: 13),
               ],
               [
                Student(name: 'Micle',age: 14),
               ]
             ]

```

I need to create a new list of list wherein each list is added by `Student` with `age` field is equal. What is the best way for the result?.