OP: I'm in a somewhat similar situation: skinny (but not very lean) when younger, and put on weight later.
I can't do high-intensity aerobic exercise--walking, and not too fast, is about it. If I do a *lot* of walking I find it maintains my weight, but doesn't seem to reduce it.
It's not the way they told us in exercise physiology class, but--at least for me--what helps in *losing* weight is weightlifting. Not a lot of sets, and medium reps--neither the 1-5 reps range (my hernias object) nor the 20+ range (can't reach any intensity with that many reps).
I don't know whether your routine permits 15-20 minutes of lifting a couple times a week, but it definitely worked for me. You may have a similar body type.
That, plus: once I'm done with dinner (which often includes dessert), I consume zero calories for the rest of the evening--no food or drink (including diet sodas, which technically have a calorie or two) except water.
These, plus a few miles of walking per day (I can't run), helped me lose 60 pounds.