If you want to get a detailed analysis of the icon of the age, as what is written, etc. - then you better give it to the icon-painting workshop. There are masters who are specially trained and know all the details, will be able approximately to tell you about your relic.
If you want to determine approximately the period is your icon, look at the basis on which it is drawn. Very old always depicted on the tree. But with this item, you need to be very careful. Indeed, in some cases, the modern painters can paint it "antique". And man, ignorant of the basics of painting and religious culture, would be difficult to determine how ancient in front of him the icon.
But on sheet metal icons produced in the 19th-early 20th centuries, Usually at the end indicates the name of the factory. If it is well preserved, it is possible to try to recover the age of the icon. The only disadvantage of this icon - it is of no artistic value. Interesting only from the point of view of historical and cultural heritage.
In that case, if you are well versed in the intricacies of different artists, painters, the age of the icon can be determined by the style of their work. Some artists of the past centuries on the reverse side of religious paintings leave certain marks. They did it in order to leave himself a reminder of who the customer is, what should be the plot of the future image and how much time he has to complete this work.
Equally important to determine the age of the icon has the technique of applying the paint. In different times it was regularly varied. Also pay attention to the primer base. It is also an important indicator of the antiquity of the image. Well, of course, the actual image. Every age has its own manner of images of images of saints. In order to understand all the intricacies, armed with a dictionary of art and begin to examine your existing artwork.