I used to believe that your age went up every year (1,2,3...) until you reached 18 and then you turned "adult" and all adults were then the same age. My Mum was quite upset when I said she was the same age as Grandma!
A childhood belief about getting older

others believed things like this
- That boys turned into women when they became adults and girls turned into men when they became adults. Anon
- I used to believe that school was a place kids go to get turned into adults.— Samantha
- That adults came into the world as adults and were never childrenAnon
- I used to think that I was smarter than adults. Now I know kids are smarter than adults in many ways— Marshall M
- I used to believe that once you reached a certain age you lost your imagination— Kiwi
- When I was young, I honestly believed that I would die before I reached high school. Anon