I confess to having struggles with my weight for many years, since around the time I left Malaysia in my late teens. My waist is now fully 10 inches wider in circumference from the 26 inches then and I am now probably at least 10-15 kilos heavier. That is quite good as I had been 14 inches bigger around the waist and 25 kilos heftier at other points in time.
Most of us have assumed, based on observations, that people tend to put on weight from around age 30-40 onwards. This is supposed to be due to a lower rate of metabolism which results in our bodies expending less energy and therefore accumulating weight through storing more fat from the food we eat.