If you want a detailed analysis of the painting including the age, value and what is written you should give it to the icon-painting workshop. They have people, who are specially trained and know all the details, to tell you all about your relic.
If you want to determine yourself about the period in which the painting was made, take a look at the basis on which it has been drawn. Very old sculptures are always portrayed in a tree. But you need to be very careful before making any judgement because some modern painters, nowadays, have the ability to paint it and can offer you as an "antique". And man, ignorant of the basics of art and religious culture, may find it difficult to determine how old the icon despite standing next to it.
The paintings made between 19th and early 20th centuries usually contains the name of the author or the area from where they belong. Only then it is possible for you to know how much old is the painting.
In the event that you are well versed in the intricacies of the various master painters, the age of the icon can be defined precisely by the style of work. Artists from the past centuries write down a note on the back of the religious paintings as a reminder of who is the customer, what should be the subject of a future image and how much time consumed in making the painting.
The technique of how the paint has been applied can help in determining the age of the painting. However, the process of painting followed a change throughout the centuries.