just number value in if-else statement in C# [closed]

I want to write some code in C# in if/else statement that user just can input number as his/her age. And if he write something else instead of number he will get wrong message.

static void Main(string[] args) 
{ 
      Console.WriteLine("Skriv en siffra"); 
      string input = Console.ReadLine(); 
      int siffra = 0; 
      bool ärSiffra = int.TryParse(input, out siffra); 
     if (ärSiffra) { 
     } else { 
      Console.WriteLine("inte en siffra"); 
     }
}