Develop a Golang application that connects to a Cassandra database, creates a table called "students" with columns for id, name, age, and grade, and inserts sample data into the table. The application should also include functionality to query the table and print the results.

Here's a simple Golang application that connects to a Cassandra database, creates a table called "students", inserts sample data into the table, and queries the table to print the results:

```go
package main

import (
	"fmt"
	"log"

	"github.com/gocql/gocql"
)

type Student struct {
	ID    gocql.UUID
	Name  string
	Age   int
	Grade string
}

func main() {
	// Connect to the Cassandra cluster
	cluster := gocql.NewCluster("127.0.0.1")
	cluster.Keyspace = "test_keyspace"
	session, err := cluster.CreateSession()
	if err != nil {
		log.Fatal(err)
	}
	defer session.Close()

	// Create the students table
	err = session.Query(`CREATE TABLE IF NOT EXISTS students (id UUID PRIMARY KEY, name TEXT, age INT, grade TEXT)`).Exec()
	if err != nil {
		log.Fatal(err)
	}

	// Insert sample data into the students table
	id := gocql.TimeUUID()
	err = session.Query(`INSERT INTO students (id, name, age, grade) VALUES (?, ?, ?, ?)`, id, "John Doe", 18, "A").Exec()
	if err != nil {
		log.Fatal(err)
	}

	// Query the students table and print the results
	var students []Student
	iter := session.Query(`SELECT id, name, age, grade FROM students`).Iter()
	for iter.Scan(&id, &name, &age, &grade) {
		students = append(students, Student{ID: id, Name: name, Age: age, Grade: grade})
	}

	if err := iter.Close(); err != nil {
		log.Fatal(err)
	}

	fmt.Println("Students:")
	for _, student := range students {
		fmt.Printf("ID: %s, Name: %s, Age: %d, Grade: %s\n", student.ID, student.Name, student.Age, student.Grade)
	}
}
```

Make sure to replace the `127.0.0.1` with the IP address of your Cassandra cluster and set the appropriate keyspace in the `cluster.Keyspace` field.

Before running this application, you need to install the gocql package by running:

```sh
go get github.com/gocql/gocql
```

Then, run the application using:

```sh
go run main.go
```

This will create a table called "students" in the specified keyspace, insert sample data into it, query the table, and print the results.