Whats the Life of a 9g servo?

Hey guys I was trying to build a plane after few months of break from the hobby, and almost none of my 9g servos work(i own like 10). It's not like all of them have been bought from the same place, many after from various different shop and cities. However all of them are unfunctional. The most recent may be like 6 months old.

Is it just the servos or could I be doing something wrong and reducing their life?