James, I’m two years older than you and feel much the same way (‘bootstraps’, ‘worn out’, etc.). Doctors’ surgeries see so many depressed people ground down by the pressures of life and it’s getting worse. I’m never that sure that knowing that many other people are feeling your pain helps but I empathise and sympathise.
Trite though it may sound at first, the simple act of regularly listing the good things in your life and the positive things that have occurred in a day can do a lot to raise mood. I recently read a post on Quora where the writer and his wife had adopted the habit of telling each other as soon as they get home something that had gone well that day and it has had a noticeable effect on their attitude and their relationship. Part of many hypnotherapy programs start with the therapist asking “So what’s been good since I saw you last?”. I too struggle with the “just having a positive attitude is enough to having a positive life” that Andy refers to in his reply to your comment. This is a more nuanced approach using real positive events rather than a synthesised emotion.