I'm 17 and it told me my mental age is 28. However, I disliked the test due to the fact that I found many of the questions to be irrelevant to maturity.
I found it particularly strange how it asked me, "How can you say that health has no importance? Maybe you've been very lucky in your life..." when I never once said health has no importance. It asked me if health was the "most important" thing in life and I simply disagreed. I never said it wasn't the second or third most important thing. In fact, I find what's most important to be a personal choice and I respect other people's decisions. I'm an atheist, but many religious people would find their religious beliefs to be the most important. For me, I find my friends and loved ones are the most important in my life.
It also told me, "Oh, boy... You're a language mangler! Darn those abbreviations!" when I find that to be irrelevant to maturity as well. Even if it was relevant in any way, I never use those abbreviations when speaking formally or composing messages for strangers to read as you can see by the way I'm typing currently and I use very few of them. I merely write them when communicating with friends via the internet because I already know my friends understand me well and it's only logical to save time typing when there's no need for further clarification or extra unnecessary letters/words. The only reason I can see for spending unnecessary time on something like that on a regular basis would be due to having obsessive-compulsive disorder. Last I checked, OCD wasn't related to maturity in any way whatsoever.
Lastly, it said, "Are you really sure to have 8 or more good friends? If so you must be a very lucky person. Good for you..." Is that supposed to be questioning my honesty and saying I'm immature for lying? Maybe it's saying the mature thing to do is be a lonely hermit. Either way, it's false to assume I lied about such a thing since, as previously stated, my friends are the most important thing to me in my life and that's why I have so many of them. I honestly love them all and I know they love me as well. Concerning the second theory for that inquiry, I don't see how being a lonely hermit would be at all relevant to maturity. If you take great joy in having friends, having none would be the illogical thing to do, assuming there aren't other circumstances affecting your judgement.
I could go back to the test and point out how most or all of the other questions on it are flawed, but I think my point is clear to most from what I've already written.