After 18, it is not the age that makes you more mature, is it? I am thinking of me at 20 and me at 30. I am not any more nature at 30 than I was at 20 for instance. Actually, I am way worse. Depressed, meaningless...out of mind..psycologically sick...etc I was much more normal when I was 20.
Anyone who tells you that they have reached the end of the road of personal development, most likely has not.
Your natural development doesn't follow some predetermined numbers or formulas. The notion that your life should magically just change once you hit 18 has always felt pretty childish to me, and ignores the reality that it's all very individual and unique to us all. I know people who, even in their 60's, still haven't "grown up", so to speak. For some, it just never happens, while there are some who are wise beyond their years. There's no point in trying to standardize us into some grey mass, it simply won't work. Back then you probably still weren't fully aware of how bad things really could be. Now you know, and it has demoralized you. This rude awakening unfortunately happens to us all. At this point, I personally would much rather just go back to being a kid.
age is an opportunity to collect more data. wisdom depends on applying logic to its interpretation, and of course, whether you actually open you eyes and collect it in the furst place. 18,12, or 21 are just arbitrary numbers. the process begins at birth, and continues until death. paying attention of course, is always a choice.