Why does this scanner not work when the data type changes?

Question

When this runs, something goes wrong when the data changes from int to String. I think.

package people;


import java.util.Scanner;

public class People {

    public static void main(String[] args) {

        String name;
        int age;
        String college;
        String petname;

        Scanner scan = new Scanner (System.in);
        System.out.println ("Enter your name:");
        name = scan.nextLine();

        System.out.println ("Enter your age:");
        age = scan.nextInt();

        System.out.println ("Enter the name of your college:");
        college = scan.nextLine();

        System.out.println ("Enter the name of your pet:");
        petname = scan.nextLine();


        System.out.println("Hello, my name is " + name + " and I am " + age + " years");
        System.out.println("old. I'm enjoying my time at " + college + ", though");
        System.out.println("I miss my pet " + petname + " very much!");
    }

}

The console produces:

Enter your name: Tim Enter your age: 12 Enter the name of your college: Enter the name of your pet:

As you can see, the third and fourth scanner run together. If the input is completed, this is what happens:

Enter your name: Tim Enter your age: 12 Enter the name of your college: Enter the name of your pet: College Hello, my name is Tim and I am 12 years old. I'm enjoying my time at , though I miss my pet College very much!

There is no error when I set age to String, so I am very confused. Appreciate any explanations.