Time is relative.
If you are 1 year old, a month is 1/12th of your life. That's a long time. I am 30 years old, which makes a month 1/360th of my life.
It has nothing to do with aging, more to do with how much time you have experienced. It works with just about anything. Imagine you've been in prison for 10 years. Then imagine another person just got to prison for their first time, and they've been there a week. To you, that person was in and out before you could blink an eye, while for them it probably seemed like eternity.