Vivaldi's Seasons premiered in 1725 and directly express, well, the seasons. Wikipedia even adds
In addition to these sonnets, Vivaldi provided instructions such as "The barking dog" (in the second movement of "Spring"), "Languor caused by the heat" (in the first movement of "Summer"), and "the drunkards have fallen asleep" (in the second movement of "Autumn").
It seems to me this direct expression of a topic is no different to Beethoven's direct expression of a topic. They just chose different topics.
So why isn't Vivaldi the start of Romantic Music?
Edit: I'm not sure how to define a Romantic piece of music, but I guess I've always assumed it was just expressing something directly, either that by itself or by departing established form.