The wrecking metabolism is really complicated and doesn't really apply to a normal person.
We do need less calories as we age. Our body shape changes as well. This doesn't' mean we can't do anything about it.
You are lifting, and say you are still a beginner, does it mean you are still lifting the same after a year? Have you changed exercises, variations on them, changed the weight? Do you feel difficulty in finishing the set or could you add 1 or 2 more reps in it? Do you have a system (upper body one day, lower body next, or push-pull,...) or you do you follow a sheet, and it hasn't changed in 12 months.
Maybe a change to strength or mixed with cardio is worth trying. Do you feel your heart rate go up and do you sweat a bit? So instead of a leg press, you do box jumps and then you can go to box jumps, step back, burpee and box jump again.
Or would you try lifting heavier and only doing a max of 4-5 reps with a 2 min rest.
Or from time to time, do sprints on the treadmill. 30s full on and 2 min rest then again 30seconds at an Olympic pace (well your version of it) and 2 min rest.
In other words, change and shake your routine.
Now to diet. 1000 a day and you putting weight on, makes me wonder if you are absolutely sure it is 1000, as in I have measured every morsel sure. Calories go up very quickly. However you sound quite determined, so it is possible.
Then, here as well, you might have to change what you eat in those 1000 calories.
I was asking about the protein bars or shakes, because I can't believe the amount of people eating/drinking them on their way to the gym carpark. Maybe watch your salt. Maybe increase the fibre, and make one meal a day a vegetables only meal. In the same way you change the workout , you change the diet, and see how you react.
We can't eat the same in our 50s then we did in our 20s or 30s. The easiest change is to eliminate sugar. Even within your daily calories. I am not saying carbs, I eat plenty of them. But sugar, nope, and sweeteners the same. This includes sauces, breads, even baked beans. You stop and read labels. I drink soya milk and very few brands are unsweetened. Protein shakes and bars are filled with sweeteners. Sugar out and fibre in. Count them as much as your calories. Put in more fibre.
So again change and shake your diet. My way is to eliminate sugar and most packages. And takeaways.
If you have been doing something for a year and you are not happy with the results, change that something. Keep lifting, but lift different and change the diet.