What's not mature about using a tool for automation?
Adults have far less free time to play games and put hours into "farming" for items to advance. Most adults are more interested in the social aspect of MMORPGs and would rather spend their time doing that.
Botting is simply automating tasks in a game, there is nothing immature about it. The idea of botting is not to directly disadvantage someone else, which are what most cheats (which I would guess are more commonly used by a younger crowd) are designed for.
The more vocal minority of botters are likely to be posting on sites such as mmowned, which are more focused towards topics of interest to the younger crowd.