Using this as a starting point from the post I wanted to write for a long time:
I found that you can trick yourself a bit into learning things if you have a hobby or other driver to spend the necessary time. If I look back at the past decade, then RPGs provided the initial momentum to get into a lot of things I might otherwise have delayed for a longer time or even never picked up - e.g. RPG streams brought me to Twitch, and subsequently also motivated me to re-activate my dormant Twitter and Reddit accounts; and though Discord feels a bit like IRC + Teamspeak for people with mobiles, I'm not sure if I would have started actively using it without RPG communities and online play; even for digital reading, the main motivation was to get an iPad was RPG PDFs and sketching maps.
And there's similar examples for other areas (e.g. doing a deep dive on Machine Learning in the preparation for a new job role, or finally getting a Smartwatch for health reasons). So I feel sometime it just needs a little nudge to get you started and after a bit of adjustment time, new things often actually don't look too bad.
I do agree, though, that this requires deliberate effort now while it came pretty much naturally in my 20s. And maybe it helped a bit that I spent most of my 30s doing a PhD, so cramming obscure stuff into my brain was pretty much required.
More generally, I am mid 40s now, so a bit younger than OP, but I have noticed some of the things other people have mentioned before. The obvious thing is readability of text, but here I can say that I held the opinion that RPG books would better be digest size and have at least somewhat larger fonts for a few years already. I have also noticed especially in the past few years that my body has settled for a generally lower energy level, so even ignoring scheduling issues, very long sessions are looking less attractive (maybe I will be able to bump it up a bit again with more exercise, but that remains to be seen). And finally, in what is probably a bit of a bleak outlook, I have estimated that at the current playing speed (one sessions per week, which is what I can confortably fit into my week), statistically speaking I have roughly 40 campaigns left until I take my final rest. This doesn't completely stop me from liking and reading new systems, but it made me realize that some big projects and campaigns will probably never happen.
Beyond that, the past few years have solidified my preference for medium-crunch systems and I ended up finding that (neo-/modern) trad and OSR systems probably work best for me, but I tend to say that's more a function of gaming age than biological age.