In my opinion, the maturity level is measured by the readiness to take the responsibility and the ability to answer the consequences. Unfortunately, sometimes it doesn't correlate with the age.
I think it has nothing to do with age! Maturity for me means that you are using your brain, thinking for yourself, tolerating others, having a morale and empathy. That has all to do with maturity, but even some children do have this ability, and some adults don't. And even physical maturity cannot be generalized, but this is a different aspect I don't want to look into here. Conclusion: In my opinion you can neither measure nor generalize maturity! I think it is a bad habit of our days, to try to measure everything, we have tables and regulations and no one can really use them. Why do we say, someone is mature or immature? There really is no use for it, I think. The same applies for many other things, however, this again would lead too far away from your topic!
I agree with Tattochka opinion
Thank you for your comments
I don't know if there is a way, but I can tell you, maturity has nothing to do with age. There are people who are 20 or even 30 and act like childs, and there are others who are even 12 and are more mature than any adult you may know.