I'm also in my 30s and have also been learning, and I recognise the frustration of trying to learn through learning specific opening lines.
What helped me was to stop trying to learn specifics outside of the first 3 or 4 moves, and just playing so much that I built up memory for specific cases where it was either a huge blunder or missed win, while at the same time sticking to trying to do the same things each game.
So I'd try not to vary my responses to particular lines so that I'd get the same situations repeatedly.
If I found myself consistently being uncomfortable, I'd change something earlier about how I'd respond, such as an early Nbd7 instead of trying to more aggressively fight for the centre in the Italian.
Overall, my three pillars of learning were puzzle rush (puzzle streak equivalent on lichess), playing more (~10k games over 2 years), and every day watching one of Naroditsky's speed-run videos, where he plays rated games from rating 400 up to around 2000 and explains his thinking. (They tend to end when he starts playing against too many cheaters).
That said, I've also plateaued around 1500 rating on chess.com. That rating is high enough for me to enjoy without feeling that every game is decided by silly blunders. I'm not sure that I have the capacity to get much higher, because my rating has barely moved for a year despite playing every day and trying hard to learn.
Strategic thinking at my level is still infrequent, but I feel like I won't progress my game until I get more of it. I've reached a level where just thinking over each move in turn just looking for tactics is no longer enough. To get better I need to think about "how to improve your pieces" which is another word for strategic and positional chess.
From watching videos, I think a lot of it is intuition. Quite often during his speed-run videos when faced of a choice of two seemingly fine moves, Naroditsky's intuition will take over and he'll say, "I'll play this move, I can't explain concretely just yet why but this other move just feels worse somehow".
There's an intuition about moves which obviously is incredibly strong in a bullet-specialist GM.
So part of it is just falling into the same tricks over and over you'll come to recognise them. Other parts is there is an intuition which as you get stronger at other aspects of the game will come to fruition.