You could ask the neighbours - assuming they live in similar looking properties, someone will know when their house was built. You could ask the local authority - they should have records stating when different properties were constructed. If your house is relatively new, you could check the one or more of the meters - there may be a date sticker on it ! If it is an older property, then the architectural style will be a give away. Failing that, post a discreet picture of it on here and someone will know roughly what era it belongs to. Local estate agents are usually quite knowledgeable as well.