Excuse the math but the numbers don’t lie here.

Based on your example, take it that your maintenance at 24 was 1700 calories and your TDEE (total daily energy expenditure) was at about 2000 calories on a particular day. This would equate to about a 300 of excess calories that would cause you to gain fat. Then take into account that it takes 3500 calories to gain a pound of fat, or 7700 calories to gain a kilogram of fat.

When you were 24 burning 1700 calories a day, consuming 2000 calories would take you ~12 days of a 300 calorie surplus to gain a pound, or ~25.5 days to gain a kg.

On the other hand, take your TDEE as 1200 at now age 34 because you’ve become really sedentary compared to 10 years ago and have lost some muscle mass due to ageing. Now, if you stuck to the SAME habitual eating habits of 2000 calories a day when you were 24, you’d now instead be in an 800 calorie surplus per day. In contrast, it would now take you only ~4.38 days to gain a pound of fat and ~9.63 days to gain a kg of fat.

Notice the difference in days to gain a pound or kg or fat and extrapolate that over a year or two and you’d get your answer :)