How much formality or informality is in this locution?

Question

In this question I asked about an aspect of a passage from a novel, quoted below.

A young man, perhaps about 18 years old, has approached a bureaucratic organization with a request that is important to him. He is directed to one of the organization's lawyers, who, after hearing his request and looking into the situation, addresses the young man as follows:

Sie haben Glück, mein Sohn. Seine Magnifizenz der Hochsekretär geruhen, Ihnen ein Paar Minuten seiner kostbaren Zeit zu widmen.

Here I will ask about a different aspect – a contrast between usages in English and German.

In English, a man with decades of experience of adult life speaking informally to a man who may be about 20 years old may address him as "son", thus a captain of a ship speaking to a low-ranking inexperienced subordinate says:

Always let a head of department do things his own way if possible. Remember that when you are a skipper, son.

In situations like this I might expect to see "mein Junge" in German.

But there may also be situations when speaking more formally – and here the only example that comes to mind is a clergyman addressing a congregant in a somewhat ritualistic context – a man may address another man as "my son".

So my question is: Given that the two persons in the first quoted passage above are strangers to each other (but also that the man who speaks is probably a couple of decades or more older than the addressee) with what degree of formality is the phrase "mein Sohn" used? The quasi-royal trappings of the phrasing of the next sentence make it seem possibly fairly formal, but the answer would appear to depend on conventions not in evidence in the quoted passage alone.

Answer 1

In situations like this I might expect to see "mein Junge" in German.

It probably depends on the relation of those persons.

Mein Sohn indicates a closer relation of the higher ranking speaker, and implicates some caretaking and courtesy.

In contrast Mein Junge, just emphasizes that the addressee is of lower rank / less experienced (but it isn't necessarily impolite).
Not much room to ask about formality.

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Given that the two persons in the first quoted passage above are strangers to each other ...

In the 1st example you given, the relation of the speaker and the addressee cannot be detected clearly¹.
It could well be that the speaker is an assistant of the Hochsekretär, who actively supports the addressee.

Worth to mention that both forms to address a (younger / less experienced) person as Mein Junge or Mein Sohn for strangers is considered to be inappropriate nowadays.
It would be noticed as a kind of disrespect, and condescending.

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¹⁾
_{In those kind of ancient, now obsolete contexts it was probably more usual to use Mein Sohn even for strangers speaking to each other from higher to lower rank, even if they are strangers.
BTW it seems to be still in use for clerical officials speaking to parishioners. The intend is often to give them a familiar and caretaking athmosphere IMO.}

Answer 2

This is a style of a former century which is in my opinion influenced by religious terms, as if the priest speaks to a worshiper. Nowadays you cannot use it, or people would think you want to imitate a theater scene or you want to muck them. When such language was used, they meant it as fatherly benevolent to a stranger.

Answer 3

The opening first sentence in the second example quote to the question currently being asked is quite formal. But I don't see a really high degree of formality when the two interlocutors are strangers when using mein Sohn.

It is more a fatherly advice and with strangers mein Junge is to be preferred (as expected by you). It is also not German spoken today and shows only the age difference in the idiom.

In sports, soccer and seafaring (skipper as: Schiffsführer, Mannschaftsführer) "formal" is not spoken anyway.