The average lifespan for a syrian hamster is two to two and a half years, but they have been known to live to four. Your hamster wont die suddenly of old age. There are signs your hamster will show as it ages.
Here is a link to an article on hamster central about old hamsters and what to look for.
http://www.hamstercentral.com/user.php? ... ticle&a=20
That being said, Hamster Central has a collection of helpful articles I think you should read. You’l find most of your questions can be answered just by reading the articles on the site.
http://www.hamstercentral.com/info.php