Simon Dendrochronology (latin) will only tell you how old the tree was - not when it was felled and installed in your house. Anyway, you can do that yourself if you can count and have one of the strong illuminated magnifying glass thingys. Mind you you'll have to be looking at the endgrain or else take a core-sample to the heart of the beam (Which might weaken it or start insect or fungus attack). To find out how long it been there you'll need radio-carbon dating... in other words how much money do you have... double it and add some more and that be just fine.. then call you local University Physics Dept. Another (cheaper) way might be to find out when the house was built? Or maybe there is a signature of the craftsman who built the house somewhere, that can be date even more accurately. Just curious as to why you need such information??? Not sure I have helped but anyway Happy New Year Andrew