using System;

using System.Collections.Generic;

using System.Linq;

using System.Globalization;

public static class Program

{

    public static void Main()

    {

        CultureInfo culture = CultureInfo.InvariantCulture;

        string format = "yyyy-MM-dd";

        int daysPerYear = 365;

        int acceptableAge = 8;

        DateTime birthDate = DateTime.ParseExact("2015-01-05", format, culture);

        DateTime returnDate = DateTime.ParseExact("2023-04-15", format, culture);       

        DateTime firstAcceptableBirthDate = returnDate.AddYears(-1 * acceptableAge);

        DateTime lastAcceptableBirthDate = firstAcceptableBirthDate.AddYears(1).AddDays(-1);

​

        Console.WriteLine("Age today: {0:N2}", (DateTime.Today - birthDate).TotalDays / daysPerYear);

        Console.WriteLine("Age on return date: {0:N2}", (returnDate - birthDate).TotalDays / daysPerYear);

        Console.WriteLine("First acceptable birth date: {0:yyyy-MM-dd}", firstAcceptableBirthDate);

        Console.WriteLine("Last acceptable birth date: {0:yyyy-MM-dd}", lastAcceptableBirthDate);

    }

}

​