That (100-200) was the difference between 25 and 55. The difference between 25 and 35 is at most 60 kcal. 60*365/7000=3.129 kg gained per year if you consume a fixed amount of calories daily every day, but almost nobody does. So if you maintain the same activity level, you'll just naturally need a bit less. If you count calories, run a BMR calculator using updated values every 5 years.

IF helps you lose weight by reducing cravings and snacking. You still need to apply CICO, IF just makes it easier to do so. I guarantee that if you consume the exact amount of calories that is required for your daily lifestyle (say 2350), you will neither lose, nor gain, weight, regardless if you eat 8 meals a day or OMAD.

Again: IF helps with cravings and hunger. You need to reduce your caloric intake (relative to body weight) as you age, but not by a lot. But obviously a 30 year old should neither be consuming as much as they were when they were 17, (and super active/developing) nor should they continue consuming as much when they're 70 as they did when they were 24, when they're likely to be way more sedentary.