i don't think it is only for kids minecraft is a creativity game and a open world with blox theme and it is also played by many big grown up youtubers!!
Vanilla beats them all in my opinion. Definitely not! I am over 30 and I play together with a friend who is around my age and we both find the game vast and amazing.
Minecraft is not only for kids, it's made to be geared towards kids (especially with the new changes they're making to have it be kid-friendly, like chat moderation, Bedrock edition marketplace, etc.) but lots of adults still use it. In fact, there's a lot of adult-only Minecraft servers that have a wide audience of people playing