Person with Protocol

Person_v4.swift

protocol AgeClasificationProtocol {
    var age: Int { get }
    func agetype() -> String
}

class Person {
    let firstname: String
    let lastname: String
    var age: Int
    
    init(firstname: String, lastname: String) {
        self.firstname = firstname
        self.lastname = lastname
        self.age = 10
    }
}

extension Person : AgeClasificationProtocol {
    
    func fullname() -> String {
        return firstname + " " + lastname
    }
    
    func agetype() -> String {
        switch age {
            case 0...2:
                return "Baby"
            case 2...12:
                return "Child"
            case 13...19:
                return "Teenager"
            case let x where x > 65:
                return "Elderly"
            default:
                return "Normal"
        }
    }
}

I'd recommend having the extension conform to the AgeClasificationProtocol, since that's where the code is. https://gist.github.com/NatashaTheRobot/2f0b83b483a49917ea04

Thank you Natasha. I missed that. I also updated firstName and lastName to constants.