Meh, it can be exciting also, you just have to keep doing new things and going for challenges.Also, you usually leave behind your carefree days where it is easy to have fun and have adventures. When you get older and are married and have children, or just have a regular job - life is no longer exciting
The problem is not the additional responsibilities, that sure make things harder anyway, the problem is that people get lazy (comfort zone) and stop trying and learning new things, so of course life gets dull that way.
It is not so easy as when you were young, that is for sure.