using System;

public class Program

{

    public static void Main()

    {

        var userService = new UserService(); 

        Console.WriteLine(userService.AddUser("FirstName", "LastName", 20)); 

    }

}

​

public class User{

    public string Name {get; set;}

    public int Age {get; set;}

    public bool IsOfDrinkingAge {get; set;} 

}

​

public static class UserData 

{

    public static bool AddUser(User person)

    {

        return true;    

    }

}

​

public class UserService 

{

    public bool AddUser(string firstName, string lastName, int age)

    {

        if(string.IsNullOrWhiteSpace(firstName) || string.IsNullOrWhiteSpace(lastName))

        {

            return false;       

        }

        var drinkingAge = 21; 

        var canDrink = false; 

        if(age >= drinkingAge)

        {

            canDrink = true;    

        }

        var user = new User{ Name = firstName + " " + lastName, Age = age, IsOfDrinkingAge = canDrink}; 

        return UserData.AddUser(user);      

    }

}