All that said, I've just been reviewing some code written by fellow not-in-their-20s engineers here and I think I'm going to have to go and vomit somewhere.
Maybe it's just fair to say that age can season, temper and improve a good engineer. It doesn't with all of them.
As an older engineer you might not get the new, cool, bleeding edge project. But then you might also not be expected to work 15 hour days.
I call that a win.
(I'm mid 30s and while I may not put out as many lines of raw code as I used to, I understand what I'm doing far better, have a good understanding of development process and tools, and place high value on robust, supportable code as compared to most of the younger engineers I've worked with recently - i.e. I'm far more productive, even if I look like I'm doing less!)