Allow creating type aliases with type checked metadata attached

Annotations in Python have many use cases beyond static type checking. I'd really like to be able to create a type that is an alias to another type while also attaching metadata to it. The idea is to be able to use MyPy's type system but also use annotations for other use cases such as runtime validation at the same time. I'm thinking something along these lines (though I have no idea how this would work in practice):

from datetime import datetime
from mypy_extensions import TypedDict
from somewhere import AliasWithMetadata

# define metadata type
Options = TypedDict('Options', {'min': int, 'max': int})
# define type alias with allowed metadata
MinMaxInt = AliasWithMetadata(int, Options)

# define age arg as type int with metadata attached
def get_rough_birth_year(age: MinMaxInt(min=0, max=120)):
    return datetime.today().year - age

# call function with int without mypy complaining
get_rough_birth_year(105)

No se identifica ningún archivo, prueba ni punto de entrada de implementación. Empieza revisando el ejemplo propuesto de AliasWithMetadata y el comportamiento existente de Python typing y MyPy; después, aclara la semántica requerida de la comprobación estática y de los metadatos en tiempo de ejecución. Para darlo por terminado, sería necesario contar con un diseño acordado y un comportamiento documentado para definir y usar este tipo de alias.