Idk how many players or forumers are above 20, but what's your reason for sticking around?
I would guess that a majority of the people above 20 have become pretty skilled at making mods or other things in the game. A lot of those people are like game developers for blockland. I'd even argue that some of the art and concept creations people have made in blockland would be successful as standalone PC games.
But I think you're selling yourself short if you're spending several months or years making a mod for blockland; you could spend the same amount of time making a game outside of blockland with the same concept and have more freedom in the design, more players, more potential for profit, and it could even become a sustainable career.
Still, Blockland is great for testing early game concepts and sometimes enjoying other people's creations, so that's why I'm still here.