using System;

using System.Collections.Generic;

var securities = new List<Security>(){

    new Security() { Symbol = "SCHW", ListedDate = DateTime.Today.AddYears(-35)},

    new Security() { Symbol = "HOOD"},

};

​

foreach(Security security in securities)

{

    Console.WriteLine($"{security.Symbol} - {security.YearsListed} {security.ListedDate}");

}

​

​

​

class Security

{

    public string Symbol {get; set;}

    public string Cusip {get

        {

            return $"{Symbol}-{DateTime.Today.Year}";

        }                       

    }

    public int YearsListed {get

    {

        return DateTime.Today.Year - ListedDate?.Year ?? 0;

    }}

    public DateTime? ListedDate {get; set;}

}