I think sometimes the milestone birthdays like 3-0 are jolting not so much because of the age achieved (which is much better than not achieved!) but because of how it makes you realize that 10 years have passed so quickly--as you are thinking back to turning 20. It feels like the years go by in the blink of an eye.

My friend and I refused to grow older at a certain point, instead we referred to our age as a hyphenated number. For example, at 52, I was 40-12