Rather than metabolism slowing down at some arbitrary age, people may tend to become less active as they get older and busier with life, yet continue to eat (or not eat) for reasons having nothing to do with hunger. It's so important to eat to satisfaction and respect appetite. If we get those things in sync, it tends to work in any decade or circumstance.
In general lately, I find I have to push my levels of comfortable fullness in order to adequately meet my energy needs. A lot of what I eat is higher volume and if I don’t get FULL my energy, hormones, and weight start dropping. The trick I’ve learned is to go for “quite stuffed” when eating things like beans, rice, sweet potatoes, smoothies, and vegetables, and to pay a lot more attention to mind/mouth satisfaction with, say, Doritos and Cadbury. If I were using my beginner understanding of intuitive eating on high-volume, plant food meals (always stop at level whatever, don’t get too hungry or full), I would be legitimately starving. And if I were applying the “gotta get FULL” mindset to candy and pie, I’d be wildly overdoing it. That’s why it’s so important to find your own way using kindness, common sense, and listening to your own body.
No rigid meal plan or set of diet rules is going to work perfectly in all situations, but your body will tell you. Once you're practiced at eating to satisfaction and respecting your appetite, you can trust that through sedentary work days, training for an event, rehabbing an injury, whatever comes up. When I was dieting, I would absolutely panic if anything about my routine changed. If the gym closed, or I couldn't go walking, or I had to rest for a week or a month, OMG! What will I do about my food?!?! It was like walking a tightrope. Now, with what I eat driven mainly by satisfaction and appetite, that keeps working regardless of if I'm bedridden, swinging kettlebells, or going through menopause. So, there's a major benefit of intuitive eating that I would never have acknowledged when I was railing against it.