You can use named parameters if you're worried:

  val emily1 = Person(firstName="Emily", lastName="Maness", age=25)

Scala's approach to constructors is a good example of convention over configuration; in Java 99.9% of classes have a constructor like:

    this.firstName = firstName;
    this.lastName = lastName;
    this.age = age;

which is just ceremonial boilerplate that obscures the actual logic of what the class is doing (an IDE can generate the constructor for you, but the person maintaining your code still has to take the time to comprehend it). You can do the more complicated things in cases where you need to, but it's important to keep the simple case simple.