Well if Lady Mary and Matthew can be worried about being childless after a year of marriage... It isn't how long they've been married, it's the age of the characters. They aren't 21 or 22 hoping desperately to have a child before it's too late.
Even the actors are older. Dan Stevens is 30 and Michelle Dockery is 31. They aren't in their early 20s, and neither are the characters. And it's an "heir" they're worried about producing for Downton's sake, not just "let's try to have a baby." They had a lot of unspoken pressure on them to produce a male heir.
If the Baker and his wife are desperate to have a child at 21 or 22, most movie audiences older than them are going to think they're impatient and overly dramatic. It's not a huge problem at that age.
"Jaws is the Citizen Kane of movies."
blocked: logan2, Diamonds3, Hamilton22