1) error

Unhandled Exception: System.ArgumentOutOfRangeException: Index was out of range. Must be non-negative and less than the size of the collection.
Parameter name: index
   at System.ThrowHelper.ThrowArgumentOutOfRangeException(ExceptionArgument argument, ExceptionResource resource)
   at System.Collections.Generic.List`1.get_Item(Int32 index)
   at FirstAssignment.Writer.TableWriter.<>c__DisplayClass11_0.<ToString>b__0(Int32 size) in F:\RiderProjects\FirstAssignment\FirstAssignment\Writer\TableWriter.cs:line 64
   at System.Linq.Enumerable.WhereSelectEnumerableIterator`2.MoveNext()
   at System.Linq.Enumerable.Aggregate[TSource](IEnumerable`1 source, Func`3 func)
   at FirstAssignment.Writer.TableWriter.ToString() in F:\RiderProjects\FirstAssignment\FirstAssignment\Writer\TableWriter.cs:line 62
   at FirstAssignment.Writer.TableWriter.Print() in F:\RiderProjects\FirstAssignment\FirstAssignment\Writer\TableWriter.cs:line 94
   at FirstAssignment.Program.Main(String[] args) in F:\RiderProjects\FirstAssignment\FirstAssignment\Program.cs:line 97

Process finished with exit code -532,462,766.

2) Program.cs

using System;
using System.Collections.Generic;
using System.Threading;
using FirstAssignment.Writer;

namespace FirstAssignment{
  
  internal class Program{
    private readonly struct Person{
      public Person(int index, string name, int age, int ageInYears){
        Index = index;
        Name = name;
        Age = age;
        Ageinyears = ageInYears;
      }
        
      public int Index{ get; }
      public string Name{ get; }
      public int Age{ get; }
      public int Ageinyears{ get; }
    }
    
    public static void Main(string[] args){
      var familyWriter = new TableWriter("id", "namn", "ålder");
      var expandedWriter = new TableWriter("id", "namn", "ålder", "ålder i dagar", "äldst", "yngst");

      var expandedContent = new List<Person>();
      
      Console.WriteLine("Välkommen till Familje-Kalkylatorn!");
      DramaticPause();
      Console.WriteLine("Låt oss starta!");
      LongSleep();
      Console.WriteLine("Vill du köra i 'Extended Information' läge?");
      Console.WriteLine("Y = Yes, N = No");
      var extendedInformation = Console.ReadLine();

      if (extendedInformation == null || extendedInformation.ToUpper() != "Y" && extendedInformation.ToUpper() != "N"){
        throw new ArgumentException("'Extended Information Mode' didn't receive a corrent input, should either be Y or N");
      }
      
      for (var i = 0; i < 4; i++){
        var printable = $"Namnge familjemedlem {i + 1}";
        Console.WriteLine(printable);
        var name = Console.ReadLine();
        ShortSleep();
        Console.WriteLine("Vad är åldern på denna familjemedlem?");
        var age = Console.ReadLine();
        ShortSleep();
        Console.WriteLine();
        Console.WriteLine("Fantastiskt, Registrerar din familje medlem nu!");
        LongSleep();

        switch (extendedInformation.ToUpper()){
          case "N":
            familyWriter.AddRow(i, name, age);
            break;
          case "Y":{
            var ageInt = ValidateAndFormatAge(age);
            var person = new Person(i, name, ageInt, ageInt * 365);
            expandedContent.Add(person);
            break;
          }
        }
      }

      if (extendedInformation.ToUpper() != "Y") return;
      {
        var oldestById = new KeyValuePair<int, int>();
        var youngestById = new KeyValuePair<int, int>();

        foreach (var person in expandedContent){
          if (person.Age > oldestById.Value){
            oldestById = new KeyValuePair<int, int>(person.Index, person.Age);
          }

          if (person.Age < youngestById.Value){
            youngestById = new KeyValuePair<int, int>(person.Index, person.Age);
          }
        }

        foreach (var person in expandedContent){
          var isOldest = person.Index == oldestById.Key;
          var isYoungest = person.Index == youngestById.Key;
          expandedWriter.AddRow(person.Index, person.Name, person.Age, person.Ageinyears, isOldest, isYoungest);
        }
      }

      WriteEmptyLines(3);
      Console.WriteLine("Tabulerar!");
      DramaticPause();
      Console.WriteLine();
      
      if (extendedInformation.ToUpper() != "Y"){
        familyWriter.Print();
      }
      else{
        expandedWriter.Print();
      }

    }

    private static int ValidateAndFormatAge(string age){
      int ageInt;
      
      try{
        ageInt = int.Parse(age);
      }
      catch (Exception e){
        Console.WriteLine(e);
        throw;
      }

      return ageInt;
    }

    private static void ShortSleep(){
      Thread.Sleep(500);
    }
    
    private static void LongSleep(){
      Thread.Sleep(1500);
    }
    
    private static void DramaticPause(){
      for (int j = 0; j < 3; j++){
        Thread.Sleep(1000);
        Console.Write(".");
      }
      Console.WriteLine();
    }

    private static void WriteEmptyLines(int amount){
      for (int i = 0; i < amount; i++){
        Console.WriteLine();
      }
    }
  }
}

3) TableWriter.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace FirstAssignment.Writer{
  
  public class TableWriter{

    private List<object> Columns{ get; set; }
    private List<object[]> Rows{ get; set; }
    
    public TableWriter(params string[] columns){
      if (columns == null || columns.Length == 0){
        throw new ArgumentException("Input Arguments are either null or none provided!");
      }

      Columns = new List<object>(columns);
      Rows = new List<object[]>();
    }

    // Adds the content rows to the table
    public void AddRow(params object[] values){
      // Input validation, throws if: The values param is null, The values param is empty, The values param doesn't match up with the columns size. 
      if (values == null || values.Length == 0 || values.Length != Columns.Count){
        throw new ArgumentException("Input arguments are either: Null, Input values were 0, or the number of Input values didn't match the number of columns");
      }
      
      Rows.Add(values);
    }

    // Gets a list of the greatest found sizes of entries in each column.
    // Aka if row 4 has the longest string, it will get added to this list as the fourth entry.
    private List<int> GetMaxStringLength(){
      List<int> colSize = new List<int>();

      // Cycles over each row and column and finds the longest possible entry for each column to determine the content width needed for the table.
      for (int i = 0; i < colSize.Count; i++){
        List<object> colRow = new List<object>();
        int greatestLength = 0;
        colRow.Add(Columns[i]);

        colRow.AddRange(Rows.Select(t => t[i]));

        for (int k = 0; k < colRow.Count; k++){
          int length = colRow[k].ToString().Length;
          if (length > greatestLength){
            greatestLength = length;
          }
        }
        
        colSize.Add(greatestLength);
      }
      return colSize;
    }

    public override string ToString(){
      StringBuilder tableString = new StringBuilder();
      List<int> colSize = GetMaxStringLength();

      // This handles and deals with formatting out rows and columns into something we can work with.
      string rowFormat = Enumerable // Creates an Enumerable (Countable)
        .Range(0, Columns.Count) // With a Range of 0-(Size of _columns)
        .Select(size => " | {" + size + ",-" + colSize[size] + "}") // Loops through the range with the columns maximum length
        .Aggregate((sum, nextValue) => sum + nextValue) + " |"; // Sums it all together

      string columnHeaders = string.Format(rowFormat, Columns.ToArray()); // Creates the formatted Header string
      List<string> values = Rows.Select(row => string.Format(rowFormat, row)).ToList(); // formats out rows and outputs them as a joint list of strings.

      // Grabs the longest row length.
      int maxRowSize = Math.Max(0, Rows.Any() ? Rows.Max(row => string.Format(rowFormat, row).Length) : 0);
      // Finalizes the final table divider line size.
      int maxColSize = Math.Max(maxRowSize, columnHeaders.Length);
      string divLine = string.Join("", Enumerable.Repeat("-", Math.Min(maxColSize - 1, 0)));
      string divider = $" {divLine} ";
      
      // Time to build this Lego Table!
      tableString.AppendLine(divider); // Adds the top divider line
      tableString.AppendLine(columnHeaders); // adds the column header line

      // Loops through all of our finalized row strings
      foreach (var row in values){
        tableString.AppendLine(divider); // Adds a divider line
        tableString.AppendLine(row); // Adds the content row string
      }

      tableString.AppendLine(divider); // adds an ending divider line
      
      return tableString.ToString();
    }

    // Prints the finalized table!
    public void Print(){
      Console.WriteLine(ToString());
    }
  }
  
}