* Species: Different species of wild horses, like Przewalski's horses, may have slightly different ages for leaving the herd.
* Social structure of the herd: Some herds are more tolerant of young males remaining, while others may be more aggressive in pushing them out.
* Availability of resources: If there are enough resources available, a colt might stay in the herd longer, but if resources are scarce, they may be forced to leave sooner.
* Individual maturity: Some colts may mature earlier than others, and thus be ready to leave the herd sooner.
In general, however, colts are typically driven away from the herd by older stallions once they reach sexual maturity, around 2-3 years old, to prevent competition for mares. This allows the younger colts to establish their own harems and start their own families.