It IS very young, but because you're that age yourself you can't see it yet.
The brain isn't fully mature until around 25.
It's only 3/4/5 years after finishing school.
Most people don't graduate uni until 21 at least.
That's 5 years or less of experience:
Independent of your parents or other parental authority safeguarding you.
As an independent tenant.
As an employee.
As someone's live in partner.
Of legal responsibility for all your decisions.
As an adult patient.
Having the physical capability to have a child doesn't indicate adulthood (children of 12/13 and even younger can conceive and give birth). Even the legal ability doesn't make it so - the age of consent is generally the very minimum a govt can get away with setting within their culture without losing votes (or worse handing votes to the opposition).
Current average life expectancy is 81 years. That's approximately 4 TIMES your current age.
I married at 23, I though I was mature enough, I thought I was "a grown up" I was not. I actually at the time thought I was leaving it too late! Because the people I was surrounding myself with at that time were also marrying and having children at this age. It wasn't until after I split from my ex and started associating with people from different backgrounds that I started to take on a different perspective. I was 31 at this point. I "did" my 20's in my 30's. Aside from my dd, yes I very much regret not listening, tying myself down FAR too young relationship wise.
But I couldn't see it at the time. You're viewing your age now from a very limited frame of reference. That changes a lot as you age.
I too think that you don't really start growing up until at least your 30's (although in the case of my ex it may be never).
You can make the same decisions and take on the same responsibilities in your 20's (partner, home, child), but it's impossible to do so with the same knowledge or confidence that you're doing what's right for you, as is possible when you're older.
That's not to say older people don't make mistakes, but I personally believe they're aware of doing so or at least of the risk they're taking (certain illnesses/disability notwithstanding).
Medically I'm glad I had dd in my 20's, emotionally I think early 30's would've been better for me and and I personally feel is a better age for most people.
Yes maturity and chronological age are different things, but one rather depends to quite some degree on life experience, which can only be acquired by living, which ageing is a natural consequence of.
Something I've noticed is a pretty good indicator is how someone behaves in an emergency. Do you crack on and deal with it yourself, call the necessary people yourself to deal with it? Or do you call your parents or older siblings in expectation that THEY will handle it for you (I'm not meaning calling them to let them know or for emotional support during/after). Sadly some people hit this point far sooner than others not due to maturity but to circumstance - ie the lack of a parental figure being available.
This does seem to happen around 30 - in my experience.
And yes, cultural comparatives make a difference too, my mother married and had me at 22, but she'd left school at 14, been working full time since then. She was still living at home until AFTER she married (my dad moved in with my mothers parents as they couldn't afford their own place) all of which was the norm for their generation, class and background... My grandparents had done almost the exact same when they first married.
It's definitely NOT old though.
I'm 46 so twice your age. To me you're only a few years (6) older than my dd. She works full time, still lives at home, likes to think she's a grown up, but still very much defers not only to me but also others older than her, she'd defer to you, she hasn't the confidence of maturity yet.
The not wanting to go clubbing - that's not necessarily a maturity thing, I've several friends that never did that, or did it for a few years & realised it wasn't really their thing. I've also quite a few friends and relatives who enjoy clubbing in 40's/50's/60's. I've only stopped because I can't stand for long so lack of seating can be problematic. I'm agoraphobic among other nonsense, but when I'm in an out & about phase (and when I can afford it) I still enjoy going to pubs, live music shows, comedy shows...
I also live in a deprived area where the average age for first child is much lower than the national average. It's where my parents are from so that too informed their perspective. I'm trying to convince my dd that she does not need to have her first at 25, which at the moment she & her friends are discussing, they think that's positively ancient! Given they've mums, aunts and older sisters who had their first (or them) at 15-20 it does seem a big difference to them.
It is much easier to travel, take risks with career, hobbies, relationships, certain experiences before you have DC. I realise that now doesn't apply to you op but for any others similar age reading not yet got DC I'd highly recommend travelling, trying as many jobs, hobbies & experiences as possible before having DC. Mainly because after DC you tend to become more risk averse, but also because you have the responsibility of ensuring a roof over their head and keeping fit & healthy to look after them/be there for them, plus they're expensive buggers!
Travel particularly broadens the mind, I'm not especially well travelled but I'm guessing I'm more well travelled than yourself.
I was given good advice once - don't wish your life away, don't be in a hurry to get to "old" - it'll come sooner than you want anyway.
It is said "youth is wasted on the young" sometimes that's true. Sometimes not.