It is effectively young to get married, at least with regard to unions in Gotha and somewhere else in all Europe.
But I have a former friend of school, old nobility, very catholic, who met her "first one*lover*» (also from old nobility) at 18 years old, and had to wait 20 years old to marry him (not even a kiss was allowed). She is 25 years old now 3 children soon 4, has totally to stop her studies. Her husband works for one year and a lot (it’s their families which supported them financially before) and evolved a lot. They will never divorce, but each can realize that they do not speak to each other and their entertainments are now diametrically set. She remains every day alone until 22 o’clock except for the weekend and even on Saturdays her husband plays tennis, frequent clubs and sometime goes in the evenings alone! She’s so sad and so old. It’s such a pity for her and for their children.
When you are young, it’s necessary to be sure to know each other already well, in particular to know yourself.