Televisions can last a very long time of you take care of them.
Especially modern televisions, that don't have the issues of cathode-ray tube degradation.
There are features of newer televisions versus older televisions, depending on when your current television was bought and for how much (price can dictate the quality of a television, often).
Higher resolutions for a better picture, more connectivity options, and bluetooth capability are just a few benefits of an up to date television.
I would say if you haven't bought one in about 15 years, it would likely be time for an upgrade, providing you have the money to do so.