This is the secret no one tells you when you’re a kid: there’s no magic age when you suddenly become an “adult”, at least not in the ways you think it will happen when you’re a teenager. The reality of being 30 or 40 is just not anything like what the 13 or 16 year old me thought it would be. I still feel like a stupid teenager sometimes but not nearly as often as I did even 10 years ago. And I have teenage nieces, which a) has not deterred me from wanting to be a mom 
and b) makes me realize I have grown up and learned a lot since then.
Sometimes I think I should be more mature by now. But I think we’re all always still learning and we all have habits or knee-jerk reactions we’d like to change, buttons we’d like to stop letting people push, whatever. To my mind, if you’re mature enough to reliably take care of yourself (emotionally, financially, etc.), know how to solve a problem/handle a crisis/find the help you need, and won’t be resentful of the time and energy and attention a child will need, then you’re certainly “mature” enough to be a mom. Doesn’t mean it’s necessarily the right thing for you right now, but in my mind it means you could do it.
Maybe the “quiz” is to ask yourself to imagine your life — right now — with a child in it. Not just the cuddling and rocking and eventual homework, but the logistics of a crying infant at 3am or a sick baby on a work day. Can you envision dealing with that? How much support from family and/or friends do you look for in your life as it is? How might that change with a child and is your network up to the task? What activities or hobbies do you most look forward to now? Would you still be able to do them with a baby? How would you feel if you couldn’t do those things anymore? What would you like to do in the next few years if you don’t have a child? Would you be bummed not to do those things? Why do you want a child now?
For me, I’ve been able to picture those changes for decades, but always with a husband. I wasn’t ready to picture doing it on my own until my late 30s and I’m now newly 42 and still trying to get pregnant. I can wish I’d been ready sooner, but I can’t go back and tell my 35 year old self not to wait — I just have to go with where I am. Interestingly, I’m much better able to do that in my 40s than I was in my 30s, so in some ways I’m much more able to deal with the difficulties and set-backs now than I would have been 5 or 6 years ago. Life is funny that way. 
Unless there’s some medical issue that means you need to move fast (assuming you’ll want to get pregnant), you do have some time to keep thinking. I think when the answers to your questions are all (or mostly) coming out with more pros than cons on the side of becoming a mom, then you’ll know you’re as ready as you can be. I hear it’s a wild ride!
Robyn
To discuss this and other SMC topics, join SMC and take part in our discussions on our lively online 24/7 Forum and at local chapter meetings.