Easy to tell - does it look nibbled? If it is being used it will have grooves, ridges etc where your budgie is nibbling at it. This will only be on one side as one face is hard and shell like and the other is very soft and can easily be scrapped with a nail.
Don't mean to be cheeky but if it doesn't seem to have been used then make sure that you have the soft face to your bird as that is what they eat the most.