You can be 10 years old and be mature enough to post (not spam) sensible and appropriate replies/topics. Your brain doesn't need to be "fully developed" to post sensible comments. Sure, it is more common for kids to be immature, but more teenagers and even some adults can be immature too.(not in brain development, in actions)
No, it's not. All I'm saying is that the older you are, the more mature you are. It's an undeniable fact, and I don't see how your trying to argue against it. Maturity isn't a switch, it's a level.
So it is true that older people are mature, but so what? RS has a age limit of 13+. So it means that anybody above 13 is mature enough for it. But you don't need to be 13 to play it. I admit I pretended I was 13 when I registered but so what? Even then, many people were far far far more immature than I was at that time. I don't know whether they were 13+ or not, but obviously most of them should be.
Basically I'm saying that you DON'T NEED to be 25 or something to be mature enough to play, even kids can be mature enough to play without spamming/doing foolish things, etc.