I don't. It's your mental capacity (well, that is what I think it is).
Think about it, even when you are 99, your mind can still be sharp and wise. The mind keeps getting new information. You know more now then where you were 10 years ago. It doesn't mean as you get older, you get more stupid.
Anyway, it is just a random made up test. Just for fun
lol I think you are misunderstanding the meaning of the test here Emilia, this isn't a test of mental capacity or how smart you are. That's an IQ test.
I think this is more of a test of your emotional age, meaning that I am the least mature one here (which I am not surprised about).