It originally meant hazy, like foggy-minded - not bright & enthusiastic, just dull, unsure, etc. Because jade is not a clear & shiny crystal like diamond. But colloquially it came to refer to someone being tired, exhausted, etc, and often also bored, since these all result in a similar dull demeanour, lacking enthusiasm.

It can have a meaning a bit similar to 'bitter.' Here's an example: "He always seems angry, because his difficult life experiences made him jaded."