Validation Across Class Hierarchies and Interface Implementations

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace SampleTest {
    public class Person {

        private string firstName;

        private string lastName;

        private int age;

        /*private string country;

        private string city;*/

        public virtual string FirstName {
            get {
                return firstName;
            }
            set {
                firstName = value;
            }
        }

        public virtual string LastName {
            get {
                return lastName;
            }
            set {
                lastName = value;
            }
        }

        public virtual int Age {
            get {
                return age;
            }
            set {
                age = value;
            }
        }

    }
}