Of course!! Anyone of any age can compete. It just means that we don't separate females or Black and/or Brown belt males by age. At those belts, everyone fights in the same age division.
"Does that mean I'll be fighting 18 year olds?" Anything is possible, but the data says it's more likely you'll be competing against other Masters-aged competitors. The average age for a brown and/or black belt competitor is 35.
There are a few reasons we do not have a Masters age class for those divisions, but the primary catalyst is simply number of competitors to create compelling division sizes. The vast majority of TCO competitors are white, blue, and purple belts. Brown and Black belts certainly compete, but in fewer numbers.
Because Masters-aged competitors are actually MORE common than 16-29 year old competitors (at our tournaments at least), you'd think it would make MORE sense to have a Masters division, right? That would seem like it makes sense, but the issue is that it leaves too many Adult competitors alone in a division with few options, and most Masters competitors wouldn't welcome them into their division. So they either move up in weight or belt, and sometimes neither option exists. And if they do, it's often not a safe jump in weight or there's a significant difference in skill. So by offering Adult only, it allows the divisions to be more robust without requiring us to continually ask permission to move a single Adult competitor into a Masters Division.