To me a lot of what middle age is about - or perhaps life in general - is accepting your life as it is, and finding a place of contentment, an angle of repose.
We often have ideas about how our life should be going, but that's not the way it's going, and we fight and fight and fight. But at some point we are taken down, usually by some bodily failure (which is where middle age comes in) and we are forced to let go and accept. I suspect that this is the seed of wisdom.
This is also the message I see regularly in Indian scriptures. Krishna says "it is better to live your own dharma poorly than someone else's well". The great statements of Vedanta say "All this is God" and "Nothing but God exists." To me, one aspect of this teaching is that if I am seeing my life as "not good enough" or not where I want to be, then this implies I am not seeing God in my life.
Sometimes this is very hard to accept.
Over the last three weeks I went through a debilitating flu and had to go through a root canal (partially caused by grinding my teeth). I took these as signs of a life out of balance and did some self-inquiry.
First of all, I was exhausted, and secondly I was stressed. This much was obvious. Next question was why.
I have just started a new job after being laid off by Sun. I didn't really expect to make this change, and I don't think I had fully accepted the change. At Sun I was working with some serious rock stars of the industry, and doing some "cool stuff" in open source. In my new job, it's a great team and fun work, but I have been unhappy because (to me) it just wasn't that "cool."
So I started trying to do this stuff on the side. Keep in mind I'm a father of 2 young kids, and I also just took away two hours from my day for commute time. So I was squeeezing this into late nights and early mornings. Thus the exhaustion. And the grinding teeth: I was pushing and pushing myself, I didn't want to let it go and just do my day job - that would be admitting surrender.
But after these illnesses and further thought and I saw that (a) this wasn't a maintainable lifestyle and (b) I was being proud and egotistical. My day job was "below me" and I was meant for "greater things." Hints of Raskolnikov. I wasn't accepting my life as it is.
It's such a fascinating process. This wasn't the first time I've gone through it, and I doubt it's the last.