An impala's age can be judged by the shape of their horns. It takes a few years to reach its final shape. This is a juvenile male. Antelopes do not lose their horns like deer lose their antlers anually.
This is a Swart Wildebeest. Note how its horns are pointing forawards compared to the Blou Wildebeest who's horns pint to the side. Notice how he was at the point of pransing. I was on foot here at the Voortrekker Monument barely a few kilimeter outside