<?xml version="1.0" encoding="UTF-8"?>
 <Ticket>
        <Age>70254</Age>
        <ArchiveFlag>вне архива</ArchiveFlag>
        <State>В работе</State>
        <StateID>6</StateID>
        <StateType>Таймер</StateType>
        <TicketID>7</TicketID>
        <TicketNumber>2018121710000019</TicketNumber>
        <Title>Название</Title>
        <Type>Билет на продажу</Type>
        <TypeID>1</TypeID>
  </Ticket>

[System.Xml.Serialization.XmlTypeAttribute(AnonymousType = true)]
[System.Xml.Serialization.XmlRootAttribute(Namespace = "", IsNullable = false)]
public partial class Ticket
{
    public ulong Age { get; set; }
    public string ArchiveFlag { get; set; }
    public string State { get; set; }
    public uint StateID { get; set; }
    public string StateType { get; set; }
    public ulong TicketID { get; set; }
    public string TicketNumber { get; set; }
    public string Title { get; set; }
    public string Type { get; set; }
    public uint TypeID { get; set; }

}

public partial class StateModel
{
    public string State { get; set; }
    public uint StateID { get; set; }
    public string StateType { get; set; }
}

[System.Xml.Serialization.XmlTypeAttribute(AnonymousType = true)]
[System.Xml.Serialization.XmlRootAttribute(Namespace = "", IsNullable = false)]
public partial class Ticket
{
    public ulong Age { get; set; }
    public string ArchiveFlag { get; set; }
    public StateModel State { get; set; }
    public ulong TicketID { get; set; }
    public string TicketNumber { get; set; }
    public string Title { get; set; }
    public string Type { get; set; }
    public uint TypeID { get; set; }

}

var node =@"<?xml version="1.0" encoding="UTF-8"?>
 <Ticket>
        <Age>70254</Age>
        <ArchiveFlag>вне архива</ArchiveFlag>
        <State>В работе</State>
        <StateID>6</StateID>
        <StateType>Таймер</StateType>
        <TicketID>7</TicketID>
        <TicketNumber>2018121710000019</TicketNumber>
        <Title>Название</Title>
        <Type>Билет на продажу</Type>
        <TypeID>1</TypeID>
  </Ticket>";
 Ticket res;
 using (TextReader reader = new StringReader(node))
 {
      var serializer = new XmlSerializer(typeof(Ticket));
      res = (Ticket)serializer.Deserialize(reader);
      Console.WriteLine($"Статус|{res.State.State}|");
 }

public class State:IState
{
    //  имплементация полей интерфейса IState
}

public class NewTiket:ITicket
{
    //  имплементация полей интерфейса ITicket
    //...

    public State State {get;set;}
}

public static class ObjectExtention
{
    public static void CopyPropertiesFrom<T>(this T source, T target)
    {
        foreach (var info in typeof(T).GetProperties(BindingFlags.Instance | BindingFlags.Public))
            info.SetValue(source, info.GetValue(target, null), null);
    }
}

var result = new NewTiket();
// копируем поля интерфейса ITicket
((ITicket)result).CopyPropertiesFrom(xmlTiket);

result.State  = new State();
// копируем поля интерфейса IState
((IState)result.State).CopyPropertiesFrom(xmlTiket);

NewTiket newTiket = xmlTiket;

public partial class StateModel
{
   public string State { get; set; }
   public uint StateID { get; set; }
   public string StateType { get; set; }
}

 [System.Xml.Serialization.XmlTypeAttribute(AnonymousType = true)]
 [System.Xml.Serialization.XmlRootAttribute(Namespace = "", IsNullable = false)]
 public partial class Ticket:StateModel
 {
     public ulong Age { get; set; }
     public string ArchiveFlag { get; set; }
     public ulong TicketID { get; set; }
     public string TicketNumber { get; set; }
     public string Title { get; set; }
     public string Type { get; set; }
     public uint TypeID { get; set; }

}

interface IAge
 {
    ulong Age { get; set; }
    ulong AgeTimeUnix { get; set; }
    string ArchiveFlag { get; set; }
 }

 public partial class TicketAge:IAge
 {
     public ulong Age { get; set; }

     public ulong AgeTimeUnix
     {
        get
        {
            throw new NotImplementedException();
        }

        set
        {
            throw new NotImplementedException();
        }
     }
   public string ArchiveFlag { get; set; }
 }

        interface IState
 {
    string State { get; set; }
    uint StateID { get; set; }
    string StateType { get; set; }
 }

 public partial class TicketState:TicketAge,IState
 {
   public string State { get; set; }
   public uint StateID { get; set; }
   public string StateType { get; set; }
 }

  interface ITicket
 {
    ulong TicketID { get; set; }
    string TicketNumber { get; set; }
    string Title { get; set; }
    string Type { get; set; }
    uint TypeID { get; set; }
 }

[System.Xml.Serialization.XmlTypeAttribute(AnonymousType = true)]
 [System.Xml.Serialization.XmlRootAttribute(Namespace = "", IsNullable = false)]
 public partial class Ticket:TicketState, ITicket
 {
     public ulong TicketID { get; set; }
     public string TicketNumber { get; set; }
     public string Title { get; set; }
     public string Type { get; set; }
     public uint TypeID { get; set; }

}