This is from a collection of classic Christmas sweaters from seasons past. Some are much older than others. These are the sweaters you are climbing through grandma's attic to find. Being that they are vintage, they each have there own history on how they made their way to our collections. That merely adds to the charm of these individual pieces of history and pieces of art. Each sweater is individual. That means there are not different sizes. All sweaters are sold as is. This one is missing bottom button, which is why its priced lower for a premium Vintage Sweater.
Model in this pic usually wears XS or SMALL for a size reference.
Keep in mind sometimes the sweaters can be in women's sizing, but customers usually don't buy them by sizes, or gender. They are unisex in terms of who wears them. Thats the point of the vintage Christmas Sweater trend. But just compare yourself to the model for reference of size.