I'm in the position you're curious about, and it seems quite viable to me. Although everyone knows, that everyone knows, that no coder can be hired over 30, none the less at least some get hired anyway. I keep assuming every job will be my last and I'll have to strike out on my own next time, and its always "A heard from B who heard from C that you're available and I've got the perfect job for your skills..." and here I go again...
"learn completely new"
That is the primary mistake. There is no "completely new". If you think "completely new" exists, go ahead, try to disprove me, go retrocomputing some COBOL on MVS, or learn this decades LISP, or this months web framework, or ...
Not going to be spending ALL weekend working on your projects once the wife, kids, house all become a part of life. Or rephrased, maybe one of your projects is going to be soccer practice with the kids. And thats OK. (edited to add, I think you will also learn the meaning of "midnight engineering" although that might only be a EE term)
My lunch hour might be an hour long but I don't need more than 5 minutes. If I'm not exercising (I hike a lot) the remainder of my lunchtime is reading / experimenting / MOOC. Also for a couple decades I've read before sleeping, although I've been told over and over that it will ruin my back, neck, eyes, sleep, sex life, and posture, but so far so good.