Thanks for all of the replies.
The article about existential depression was great! I will be re-reading it very closely when I have time to take it all in. At the quick glance I have had, I particularly liked the characteristic strengths and associated difficulties for gifted adults. This helped to explain a lot of my "quirks" and frustrations.
I also agree that personality does play a part. I am an introvert and definitely not suited to any type of executive role. I am also a bit of a perfectionist but have been mellowing as I age.
The point about how intelligence lives in day-to-day life was interesting, as I had not considered this before. I do certainly benefit from my intelligence in everyday tasks but had been taking it for granted.
Onto the challenge and boredom.... I am quiet and easy going. At school I remember completing the set exercises and then waiting (or working ahead a little in the math text book - just consuming time with practice questions when I had mastered the concept long ago). I don't recall being bothered by this though - it was just the way it was. I don't remember being challenged and I wonder if this is where the problem lies. I have learnt that I don't have to "try" - no perseverance, drive etc. I've also previously not attempted difficult things for fear of failure.
At my current job (and my previous ones too), I guess I just do the same amount of work my peers seem to do. Then I spend the rest of my time researching topics I am interested in (which change all the time). I have never applied myself and this is what I am kicking myself about. I have had plenty of time to become a specialist in a particular field (which would earn double my current income), but I haven't. Of course, I enjoy the flexibility of my job and being able to do what I please. But I also see it as a bit of a dead-end, as there is no career progression. I'm not sure if I want to spend the next 30 years doing what I am doing now.
I guess I need to figure out what I want, set myself some goals and step out of my comfort zone. Thank you for that advice and making me realise that I can do more, if I want to.
