When kids grow up into adults, they do not always become massively different persons in their core. Oftentimes, creative kids grow up into creative adults. Their hobbies often remain or they still look back fondly on their old hobbies. And when they are bored, they sometimes go back to their old hobbies, due to nostalgia. You see it everywhere, in music people listen to, books they read, etc

All of that is ok. Plus, majority of lego kits go to kids.