You also got older ... Age is a factor.

Does weight increase as you get older if you consume the correct amount of calories?

Weight will increase as you get older if you consume a constant amount of calories. Your metabolism slows with age (and generally entering the job market means a much more sedentary life style for most white collar workers).

So you adjust your calories

Calorie counting is a habit that's generally unnecessary as a teenager so it's a habit not everyone is familiar with.

Easy to say difficult to do. Most people have family, work, 100's of tensions etc.. Reducing calories might not be that much of priority.

People tend to have more major life events as they get older, and sometimes they choose to soothe with food when facing major loss in other areas.

No, but the 'correct amount of calories' is a steadily decreasing number, so it requires constant adjustment.