Though my modest adventures aren't nearly on the scale of Andrew's, I feel I had a good run in my 20s to early-mid 30s.
Around 35 (I'll be 38 this coming year), something clicked where having a significant other in my life, working a little more of a career vs. a job, etc seemed like a good fit for me.
So, now I am in the mode where I hope to get to the point (fairly soon; as within three to five years) where I can take off for 6-8 weeks at a time as opposed to 4-6 MONTHS at a time.
Before, I'd be in the mode of "Work hard for two years, live frugally, save money, quit. Go hiking".
Now, I'm the mode of "save money, live modestly, build up my skill set, quit working full time and go hiking".
I have no regrets of how I lived my life in previous years. It was the best fit for me through the formative years of my adult life.
Now that I am engaged, working a so-called 'professional' job  and so on, I don't feel any more grown up, just doing something that feels right for this point in my life. I do not necessarily want to live a fully nomadic and light lifestyle.
Not to say I don't do things I love. Good luck getting hold of me on a weekend. And my horded vacation time is usually spent in the backcountry. (But, as mentioned, that should change in the future.
Truly living an adult life is living the life YOU want to live and being responsible, self-sufficient and content while living it.
I see too many people living an adult life of mortgages, kids and a job who are miserable. Is that adult? OTOH, living in Boulder, I see many people who mock the life I just described but will happily cash the trust fund checks from their parents.
Neither is an adult life.
The person who loves their children, enjoys their home and cherishes their week long backpacking trip is living an adult life.
And the 50 yr old river guide who never married, lives a modest lifestyle that affords a life she loves? Well, she is living an adult life too.
So, let's put away the labels.
Let's all hope we live the life we want to lead.
That, my friends, is truly the adult life.
 I really do loathe that term, but people know what you mean when you say that. My Dad, a recently retired sheet metal worker, was a heck of a lot more professional than some of the whiny 'professional' bozos I know who show up late, slack off their work and have a huge sense of entitlement. But I digress. :D
Something related I wrote a few years back. Really need to update it for my current life!
Post Trail Adjustment