https://codesandbox.io/s/is849

edit: complete code

```typescript

class Person { id: number; name: string; yearOfBirth: number;

    constructor(id: number, name: string, yearOfBirth: number) {
        this.id  = id;
        this.name = name;
        if (yearOfBirth < 1900 || yearOfBirth > 2020) {
            throw new Error("I don't understand you. Go back to your time machine.");
        } else {
            this.yearOfBirth = yearOfBirth;
        }
    }

    getAge(): number {
        const currentDate: number = new Date().getUTCFullYear();
        return currentDate - this.yearOfBirth;
    }

class Dog { id: number; name: string; yearOfBirth: number;

    constructor(id: number, name: string, yearOfBirth: number) {
        this.id  = id;
        this.name = name;
        if (yearOfBirth < 1947 || yearOfBirth > 2020) {
            throw new Error("I don't understand you. Go back to your time machine.");
        } else {
            this.yearOfBirth = yearOfBirth;
        }
    }

    getAge(): number {
        const currentDate: number = new Date().getUTCFullYear();
        return (currentDate - this.yearOfBirth) * 7;
    }

const buzz: Person = new Person(1, `Buzz`, 1987);

const airbud: Dog = buzz;

console.log(`Buzz is ${buzz.getAge()} years old.`);

console.log(`Airbud is ${airbud.getAge()} years old in human years.`);

```