Thats a nice old skeleton key.As far as determining what it went to,I am not sure that you could ever find out. Maybe someone more knowledgable on keys may be able to give you a rough estimate of the age.
I am a locksmith by trade. This looks like a furniture or cabinet lock key. They are still being made like that so age could be hard to determine. These are called Warded keys. If the end is hollow, then it is a warded barrel key. If the end is solid and is slightly extended beyond the ward, then it is a warded post key. Most likely it is for a chest or other piece of furniture.