Stress sure is a strong factor. Weird that it lies in the perception of the world, in the mind. And has really almost nothing to do with real physical world, other than being the change between what the brain is made of (but then again the entire world we perceive is change between something... just as are we ourselves; nothing is standing still, everything is in constant, neverending flux - it's the necessity of existence). Second to diet really, I'd say, and physical exercise being the third.
I've "mastered" stress years ago, getting ever better at it since (and I'm 23...), even before finding out about diet. There's really no point stressing over anything... stress comes from not realizing you cannot change something to something you'd rather have, just have to accept, look into the future and future possibilities, and just move on. Dwelling on the past is, honestly, idiotic if there really is nothing you can do about it. The present and, most importantly, the future matters, not the past (might be some rare exceptions).
Just do what is life's core quality - move on.
