Straight talk needed! Do rules change after 50?

Weight fluctuates. That's just reality.

I am over 50 and don't do low carb or 1200, and I lost just fine. (I'm afraid I wouldn't last five minutes on 1200 calories, but that's beside the point.) When you say you "watch portions" - do you weigh your food? Doing so will give you more accuracy and peace of mind if scale fluctuations are bothering you.

I'll be 50 later this year. When I started lifting weights again last fall, my weight shot up seven pounds. This all (plus more) came off over a few weeks.

One age related thing I do know - I'm a lot less strong than I was 11 years ago when I was a full time yoga teacher. Having more muscle does make it easier to lose weight. I plan to keep up the strength training / bodyweight exercises forever.

If you go from low carb to not-low-carb and/or do 2-hour workouts, you're going to see some water weight gain. Ignore it.

I am well over 50, and the formula CICO works just fine for me as I have been consistently losing since October last year. Your experience is one of the many reasons I do not weigh myself every day - actually, I only weigh maybe every 4-6 weeks. There are too many influences for me to feel confident that a daily weigh in is an accurate reflection of whats really going on inside.

Another perspective on age (and other things) and metabolism:
http://www.fitmole.org/8-ridiculous-myths-everyone-believes-about-their-metabolism/

I'm in a similar boat. 54 and petite, (stats:54, 5'1, GW 120).
Ditto what @PaytraB wrote: "I've gained a few pounds recently but that's from overeating, not being over 50."
I don't think there is a rule change w/"50". However, In my case, post-menopause did effect hormone levels, so there was a lot of flux going on with how the body stores and burns fat. It did have some impact on moods, energy levels, ability to keep focused and diligent. The biggest factor for weight loss was eating at a healthy deficit, maintaining muscle stregth. Yea, take a deep breath, keep experimenting and you will find what works for you over the long term. Sounds like you are on the right track, finding out what you can live with long term.

High carbs, working out, cardio will retain water weight as everyone has already said. The 200 calorie difference isn't going to matter given the 2 hrs of working out. With intense levels of exercise you will need more carbs, fats and proteins to keep your energy levels up. I prefer the extra protein for workouts, I find I feel more energy per calorie. Continue to accurately track macros, adjust as needed. (weigh food, don't subtract out workout calories since people tend to overestimate that.)
I just came off a plateau of 6 weeks (which I know seems like "forever"). I think of it as my re-composition phase.

Losing weight at 50 was much different for me than losing when I was younger. Partially due to lifestyle changes and partially due to hormonal fluctuations. Fat loss will always be about calories, but that doesn't mean calories is the only factor to consider.

Regular cardio exercise was the biggest help to me. It helped control hormone fluctuations and water weight. I have lost about 30 lbs. but it wasn't as easy as when I was younger. Not at all.

It sounds to me like water weight. Probably from re-introducing carbs and DOMS from training.

¡Cálmate!

Short answer: No, the rules do not change.

You burn fewer calories as you lose muscle mass. Most people lose muscle mass as they age purely as the result of not using their muscles much over decades. Even people who are very active in their teens and 20's often get less active as they get older. But gain muscle mass, and that "metabolism slows down" thing pretty much goes away.

Changes in hormone levels do affect your metabolism to a some degree. There is some evidence that the loss of estrogen does make it harder to lose fat in the abdomen (but not anywhere else; sucks, right?), and that higher estrogen also help women build muscle a little more easily. HOWEVER, neither of these effects is strong enough to account for the inability to break down fat or build muscle with the same kind of diet and exercise that a younger woman would use. You might just end up with a skinnier butt and a little tummy, though. Or, as alot of the women here can proudly show you, you might not.

For me, the biggest challenge with being 50 is the little aches and pains that make me feel like not moving, or like curling up and eating comfort food. But, I also know that more I move and the better I control my weight, the better all those little things are going to feel.

The question is "do the rules change after 50?". But for the fact that nagging little injuries don't go away as quickly any more, no. You eat at a deficit, you lose weight. Eat at a surplus, you gain weight. You do cardio, you gain endurance, your "wind" is better and you feel better. You lift weights/do resistance training, you gain/don't lose as much muscle, get stronger and look more "toned". Pretty much as happened before getting to 50+.

If you have DOMS, and even for a week or so after it goes away, you are retaining water especially since the increase in calories was small.

You said you know it's not fat, so leave it there. People of all ages fluctuate on a daily basis.

Here is the straight talk you asked for:
I'm 60 yo and have lost 130 lb with 20 left to goal. I hit a new low yesterday. Today I'm up .6 lbs. I thought I would be up more than that to be honest. I've fluctuated within a 4 lb range in the last 7 days. This is completely normal. I weigh daily, enter everything into Happy Scale phone app, and visually see a graph of my trends and fluctuations. I can pretty much predict when my weight will go up or down just by looking at the past patterns.

Yesterday I weighed first thing in morning like I always do, then weighed again after my personal training workout, just to compare my weight to the one at the studio. (I rarely do this.) I went up 5 pounds between 7am and 10am!!! Some of it was gym clothes, breakfast, & water, but not 5 lbs worth!

Where did the extra weight come from? Who knows! What did I do? Shrugged, took my shower, and went on with my day! This morn, as I said before, 4.5 of that was gone and I sm up only .6 from yesterday morn.

I asked my hubby about it, he's a dialysis nurse and deals with water weight on patients all day long. He just looked at me and said there is no explanation. Even when they remove a known amount of water from a patient in a 3 hour dialysis session (which is the purpose of dialysis), the change in the patient's weight does not always change the same as you would expect it to mathematically. It's the human body!

We get more sedentary as we age, typically. Often, we're sitting at desks instead of waiting tables or working in retail, we're not chasing kids around, we're not dancing at nightclubs til 2am, we pay someone to wash our cars and mow our lawns and maybe even walk our dogs and do our shopping.

Plus the body does less cellular regeneration. It all adds up to less calories burned.

Just a recommendation look into intermediate fasting or the 5:2 diet.