You need to treat it differently to losing weight when you're younger. It's not your metabolism as such, but your hormones (bloody fucking hormones!). It's not TOO hard, that's an excuse we tell ourselves to avoid trying. It's not even harder, it's just different.
I've been 'getting healthier' since I hit 50 (2 years) and my body shape changed completely. Stopped 6 weeks ago because WFH went nuts and I fell off the wagon. I've only put on 4 pounds, but lost all my muscle mass and my waist grew 3 inches. THREE fucking inches!
Bloody meno-belly!
So back on the wagon I go!. I try to do 3 sessions of weight training and one strength training class (pump or bodypump or bodytone) a week. So only max 4 hours out of my week. If I'm going anywhere within a 20 minutes walk, I walk. No more pretty uncomfortable shoes! If I can't walk in them, I don't wear them. 
I read for over 50s it should be weight training rather than cardio sessions. Cardio burns calories while you do it, building muscle helps to continue burning afterwards. (And who wants to be doing star jumps with dodgy knees - or hips in my case.) If you actually like sweating then Tabata sessions are very short and can be low impact - 5 minutes warm up and 5 minutes going for it. Every exercise you'd ever need is on YouTube. Find one where you don't want to kill the instructor
and start slow.
You don't need to do a long walk, you can spilt it up as long as it's about 15 minutes where you're out of breathe by the end (but can still talk) a couple of times a day. Even better if you find a hill.
I'm a grazer, snacker and huge portion person too. Lately I've been keeping a food diary. I don't log calories etc (cos honestly who has the time to work that out!), just write down everything- no matter how small. If I want to eat between meals, I have to write it in the diary BEFORE I can have it. Makes me think do I really want this or am I mindless eating?
The only way I can control portion size is use smaller plates/bowls. Big plates with 'small' portions and lots of empty space allow me to trick myself into thinking I'm being deprived and can have seconds or a snack later. A full small plate tricks me into thinking I've eaten enough. I write down whether it is a regular size (small to me lol) or large portion of veg/meat/carbs. I don't go into any more detail because my issue isn't the type of food, it's the amount of it.
Go slow. Don't look for quick fixes, and quick results. Don't think diet, think healthier. 1 to 1.5 pounds lose a week. We all get excited when we strict diet and lose 5 pounds in the first week and then when we can't sustain that rate we give up and bam those 5+ pile right back on. And we're pissed off and start believing it's pointless. Accept some weeks we'll lose nothing, but keep going. Being resilient and believing it can happen are the major factors in getting healthier, feeling better and looking how we want to.
Sorry off that comes across as healthy living guru bollock. But it took me a long time to figure out what works for me after years of a cycle of a months diets/exercises/promises to my self followed by dramatic wagon falling off and then a year of saying what's the point before starting again.