I read somewhere, that psychologigal Depression is a necessary part, of the Old Soul's life.
Maybe it could be also short times of Depression, during the day. For example 2 times 20 Minutes every day, in average.
Does the MT includes this Thesis, too? (The first sentence)
I don't think Depression is a necessary part of an Old Soul's life and no, Michael never said this. They said it is the only neurotic manifestation left to the Old Soul, i.e. they do not suffer from other psychological problems. I don't even know if I agree with that, I know couple of Old Souls, and they definitely have issues. They are not issues that need psychiatric treatment, but issues they are.
And 2x20 minutes a day is not terribly bad, but its quite a lot. The last time i felt depressed was last year March, for just a few hours.
Depression could have all sorts of causes, including what you eat, how you relate to yourself and others, how you express yourself, and I don't know what else. If its anything eating related, then that is easiest to try to test, by cutting out some most suspicious foods, like sugar, E numbers, wheat and anything else that is known to be problematic. It would be easier to try to cut one at a time.