That is a cute gosling but other than vet sexing no one can tell just by looking at it. Metzers web site tells you how to vent sex. and in case you'd like infop on how to care for it this is on ducklings but at the age your gosling is it fits them too, other than gosling like greens at an early age. https://www.backyardchickens.com/t/750869/raising-and-caring-for-ducklings#post_10611711