I wish people would add their ages to this. For frame of reference, I have worked out my whole life - athlete and athletic, decent genes. I am 5'7"
In my 20s, I could drink and eat whatever I wanted and I weighed 122 pounds. I worked out 5-6 days a week - heavy lifting program.
Once I hit mid-30s, I could not eat the same way I did in my 20s. I watched what I ate during the week and was strict about routine eating (same breakfast, snack on vegetables, etc) but I did what I wanted on weekends with no real issue but my weight was now holding at 130.
I had three pregnancies and gained weight with all of them. Still exercising, even distance running added to strength training, boxing, tabata classes, etc. But after babies a little extra and 140 and fine with that.
Now I am 50 and just went through menopause and WTH -- I am 156 and cannot lose weight if I tried. Seriously. Eating healthy and calories are limited, exercising, strength training, incorporating extra movement (walks between 2-5 miles, etc) ZILCH.
I know that this is a struggle for others, but I have never encountered this until menopause.