I am making an assumption that the extinguisher you are referring to is a halon (or the FE241 type) of built in system. If that is what you are talking about, they are supposed to be checked every year. That means taking the bottle out and weighing it. There should be a weight on the bottle. You can look at the indicators to see if the bottle is charged, but they are not absolutely accurate. The only way to ensure that it is charged is to weigh it. If the last time it was checked was 2007, you are way overdue for a check. You can take it to a fire extinguisher company and they can check it for you.
Handheld disposable extinguishers have a life of 12 years. The manufacturing date should be on the label or stamped into the bottom of the bottle.
