string Gender = "";

while(true)

{

        Console.WriteLine("Enter your gender (male or female): ");
        string GenderTry = Console.ReadLine();
        if (GenderTry == "male" || GenderTry == "female")
        {
             Gender = GenderTry;

             break;
        }
        else
        {
             Console.WriteLine("Error! Enter your gender again");
        }

}

Console.WriteLine("Your gender is: " + Gender);