It's funny that you quoted this line because I think it reveals a particular ignorance that the author has, namely a misunderstanding of depression due to her particular experience with it. A more truthful version, in my view, would be the following:
When you’re not depressed, you want things: work, love, children. When you have mild depression, you want to want things. When you’re deeply depressed, you no longer want anything.
Age really doesn't have anything to do with it.