Plus, the number of milestones and changes that occur when you are younger are much greater then when you are older, and those changes are more novel. You have your first word, your first step, your first day of school, the first time you learn to ride a bike, the whole puberty thing. There is a huge number of changes occurring that you have never experienced before. Plus you have the anticipation of all that is to come, and when you are focused wanting something to be here, it feels like it takes much longer to arrive.

As an adult, I often have days when I become so involved in what I am doing that I lose track of time, poof all of a sudden the day is over. The only time I can remember that happening when I was younger was when I was either reading or playing video games.

Good point. Seems obvious in hindsight although the article also presents another theory: "the monotony of the events of old age compared with the vividness and novelty of the experiences of youth must also be considered."

Yes, at 35, this is how it seems to me, too.