Every baby is different, thus, teething ages can differ greatly. Most babies begin teething sometime around 4 months, while others could be considered early or late teethers; some babies are born with teeth and others are a year before first tooth!
Best answer I can give you is to look for signs & symptoms of teething...increased drool (although mine was never a big drooler), swollen, bumpy gums, increased gnawing or gumming of objects, etc. Many babies will also "teeth" for an unspecified amount of time before tooth actually appears.
I wrote a hub about this that you can read if you like. Hope this helps!