That, AND being less active. It's both.
Especially these days when often the only activity people do is stare at a screen.
The screen needs a good talking-to quite often.
Women have one factor that messes with metabolism that men do not have to contend with.
Pregnancy.
Yes, it is possible to maintain a decent weight as you age, but both men and women will put on weight in the process. It happens.
But having a baby is at least a better reason for weight issues than a beer habit.