True about the lack of title in "Herr von Katte", and yes, son of General in his 50s would still be way too old.
Conventions: good grief. Sadly I never read the legendary "Knigge", aka the Prussian etiquette book spelling this out, and have to go by what various letters and novels (written in past centuries, not in the 20th or 21st!) tell me. Good old Fontane comes in handy again, what with being THE Prussian novelist, even if, as one critic memorably put it, he's sunset Prussia, while FW is Dawn Prussia and Fritz of course is sunrise and Prussia: High Noon.
Anyway. If you were a fellow noble, you might introduce someone as "von X" to someone else, but thereafter you only use the last name. (You do this with non-nobles, too, btw.) So in Fontane's most famous novel "Effi Briest", the heroine is actually born "Effi von Briest". She later marries Geert von Instetten and has an affair with one Major von Crampas. Throughout the novel, Effi's father is "old Briest", no one, including the narrator, says "von Briest", whereas her mother is always "Frau von Briest", just as Lehndorff refers to his cousin as "Frau von Katte". Her husband and her lover, who have served in the same regiment back in the day, call each other "Instetten" and "Crampas", and Effi before her affair with him calls Crampas "Crampas", too, when they start to be on friendly terms - when she's first introduced to him, she calls him by his military title of "Major". (Much later, when the affair is long over but gets discovered by accident, Instetten tells his bff (von) Wüllersdorf to go and challenge "Major Crampas" in his name to a duel; the lack of "von" isn't meant as an insult, it's the habit. Effi's only friend in the small town her husband is the chief Prussian official of is a non noble excentric apothocary by the name of Alonso Gieshübler. (Yes, he had an Italian mother.) Everyone, including Effi, calls him "Gieshübler".
I would say "Prussians are really into last names", but it's actually not much different for the Austrians. MT in her letters to her former lady-in-waiting and friend calls her "my dear *last name* and "dearest *last name*", not "Sophie". (No "von" at all.) Basically, if you're not the monarch or one their siblings, your first name doesn't get used by anyone ever. At least not if you're a man. (Effi's mother adresses her father with "Briest" consistently, while he calls his wife "Luise". )
Re: Kattes
Conventions: good grief. Sadly I never read the legendary "Knigge", aka the Prussian etiquette book spelling this out, and have to go by what various letters and novels (written in past centuries, not in the 20th or 21st!) tell me. Good old Fontane comes in handy again, what with being THE Prussian novelist, even if, as one critic memorably put it, he's sunset Prussia, while FW is Dawn Prussia and Fritz of course is sunrise and Prussia: High Noon.
Anyway. If you were a fellow noble, you might introduce someone as "von X" to someone else, but thereafter you only use the last name. (You do this with non-nobles, too, btw.) So in Fontane's most famous novel "Effi Briest", the heroine is actually born "Effi von Briest". She later marries Geert von Instetten and has an affair with one Major von Crampas. Throughout the novel, Effi's father is "old Briest", no one, including the narrator, says "von Briest", whereas her mother is always "Frau von Briest", just as Lehndorff refers to his cousin as "Frau von Katte". Her husband and her lover, who have served in the same regiment back in the day, call each other "Instetten" and "Crampas", and Effi before her affair with him calls Crampas "Crampas", too, when they start to be on friendly terms - when she's first introduced to him, she calls him by his military title of "Major". (Much later, when the affair is long over but gets discovered by accident, Instetten tells his bff (von) Wüllersdorf to go and challenge "Major Crampas" in his name to a duel; the lack of "von" isn't meant as an insult, it's the habit. Effi's only friend in the small town her husband is the chief Prussian official of is a non noble excentric apothocary by the name of Alonso Gieshübler. (Yes, he had an Italian mother.) Everyone, including Effi, calls him "Gieshübler".
I would say "Prussians are really into last names", but it's actually not much different for the Austrians. MT in her letters to her former lady-in-waiting and friend calls her "my dear *last name* and "dearest *last name*", not "Sophie". (No "von" at all.) Basically, if you're not the monarch or one their siblings, your first name doesn't get used by anyone ever. At least not if you're a man. (Effi's mother adresses her father with "Briest" consistently, while he calls his wife "Luise". )