My wife and I are 57 years old, so I think I can address this. We finally got the younger child through to grad school and paid off all our debt, and now we can devote our time to what we want to do. Mostly, anyway - I'd like to be doing coding for pay, but instead I do technical translation.

But in terms of study - academic work - we're free. She's got a PhD in theoretical physics and has finally had the time to start publishing, including picking up quantum chromodynamics.

I've picked up my original doctoral work, too, which was on hold for thirty years while I supported the family. I've had no problems whatsoever tackling difficult topics - in fact, I've had less difficulty. I'm calmer, partly because I have to be in order to keep my blood pressure under control. I think I can do less in any given day, but I'm not even sure about that, because when I look back at items checked off over a week or a month, it's about what I wanted to get done.

So putting off study until you're 55 is not a bad plan. Keep reading about things in the meantime, of course. Take good notes. Keep things where you can find them in ten or twenty years. Write down your daily thoughts. You'll thank yourself later, trust me on this.