Specifying a custom equivalence relation for sets

custom-equiv-set.scala

case class Person(name: String, age: Int)

val p1 = Person("Mads",22)
val p2 = Person("Mikkel",22)

implicit val eq: Equiv[Person] = new Equiv[Person] {
  def equiv(x: Person, y: Person) = x.age == y.age
}

Set(p1,p2) // Set(Person(Mads,22), Person(Mikkel,22))

Set(p1,p2)(eq) // should give Set(Person(Mads, 22)) but it doesn't work

FYI: I ended up projecting out the property I wanted and added that to a set.