You'll be happy to hear this is pretty simple to find out!
If you have lost the deeds to your property you should inquire with the land registry to get a new copy of them.
You can also check with the solicitor you used when buying the property, they may have kept a copy.
There are other ways you can check how old a property is. Look at the features and design of the house.
Hope that helps you out.
Jonathan Rolande :)