I suppose it means different things to different people. Part of the pleasure in life, at some stage, is feeling yourself to belong to a hip movement, a little group of people who know where it's at. (What it is nobody really can tell you.) Fashion photography offered that for a while, and so did calendars, and there was a definite buzz going down to London and holding castings etc. with much of the joy being in the fact that somebody else was paying you to have your kicks. I loved going abroad on trips. Usually, but there were one or two best forgotten.
That may or may not end with age - the enjoyment, I mean, but what does happen is that when that work does end, which for most of us, especially in modern economic times it will, the absence of it is almost physically painful.
Yes, the sense of running out of time comes along too. It hit me about a decade ago, and brings a new set of pressures which are often outwith our own control. It forces one to accept that responsibility isn't limited to self. It's not about work, though, it's about not leaving a mess behind one for others to have to sort out. My aim is to be able to close my eyes for the last time knowing I did what I could to leave things tidy. (You should see my office - that's the exception: it will never be tidy!)
In the end, you do what you can.
Rob