Is "ex-" (old, past) seen in Latin

Question

I just really don't know where English ex-, as in "ex-friend" exactly came from. So far I havent seen such meaning in Latin (or Greek), but I know little. It would bolster the following idea, if there were the slightest hint of such a meaning in Latin. In the majority of cases it means "out, off, from", which is perhaps close enough, so I'm just asking for curiosity's sake whether "ex-" could mean "old", not just "former", specifically.

I reason thus:

• Indo-European s-mobile is as of yet unexplained, because it appears and disappears without a discernable pattern prefixed to various words in various Indo-European languages. One usual example is taurus ~ En steer. I entertain the idea that *s- was one or various prefixes. I quickly found that *(s)- sometimes corresponds to German aus- "out, off" in a couple of synonyms, and I fixated on the idea that it might be a reduction from "ex-". Not to divert, it doesn't make much sense for a bull to be out. But it would make sense as an ex-taur, e.g. if a steer were a castrated or grown bull; On the one hand, a grown castrated male cattle is rather called ox. On the other hand, indeed, there's the adjective Ger ausgewachsen "grown up". Also, Jung-Bulle is a fixed term, but Jung- is generally productive (linguistically; no pun intended).

On the topic of age, senex came to mind, and I wondered if folk etymology would be liable to split the word and deem the coda the semantic mark.

Goth. sineigs reconstructs PIE *senikos [Kroonen], though all the remaining languages reflect *senus. Just noting, because en.wiktionary doesn't though it seems relevant to senex. They have derived PIE roots from less, so either there was a reason to leave senex with *senus and imply a Proto-Italic development instead or most likely they just didn't catch up with the book-keeping.

• By the way: Also cp. G sehnig "sinewy; (of meat) gnarly" (which is indicative of its lived age? Obviously, usually compared to Sehne "tenon", sine, sinus); synonym: zerrig (cf zerren), perhaps figuratively störrisch "stubborn" (cf PIE *ster- "stiff", G starr, stur) though usually said of living animals (for which, incidentally, DWDS gives a similar sense under v. G. zieren, which I likened to tired [discussion]).

• By the way: "ex-" is difficult to reconstruct for PIE, giving slightly different alternative forms, and it's one of the very few roots (or paradigms) with an initial vowel.

Different derivations for an s- have been gleamed, and I might be way off anyway. So if the answer is negative, that's expected.

• By the way: cp expectation, Ger Aussicht (lit. "out-sight", "out-look"); Should it be "ex-spect" or did German frequently produce phono-semantic calques or severe folk-etymology?

Lest I be blamed for omitting the question: Is there a phrase, fixed collocation, or even a word that meaningfully compounds a) "ex" and "taurus" in any such way as outlined above, or b) about any other stem with "ex" in the sense "mature, old"?

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Basically I was just surprised that Wiktionary gives such a terse gloss for Lat. prep. "ex", because out turned out very polysemous. After all, however, they just need to link [[ex-#English]] directly to the Latin prefix that gives a couple more glosses, which are a better fit, for a start:

2. throughout

ē- + dormiō → ēdormiō

ē- + pōtō → ēpōtō

3. (intensive) thoroughly

ē- + dūrus + -ō → ēdūrō

ex- + acuō → exacuō

4. denoting achievement

ex- + ōrō → exōrō

ex- + pugnō → expugnō

...

Answer 1

This is what the OED has to say on the subject:

[On the analogy of forms of expression like ex exsule consul, ‘(that has become) a consul from an exile’, the phrases ex consule, ex magistro equitum, etc. were in the Latin of the empire added as titles to the names of men who had filled the offices of consul, master of the horse, etc. At a later period these phrases gave rise to the compounds exconsul, exmagister, in the same manner as the compounds proconsul, propraetor had been developed from the older pro consule, pro praetore. In medieval Latin this usage was greatly extended, such forms as ex-Augustus (‘ex-emperor’) being of frequent occurrence. Some words of this formation (e.g. ex-professor) passed in adapted forms into Italian and French, and on the analogy of these ex- was prefixed to Romanic words. The English use, imitated from French, seems to have first become common towards the end of the 18th cent.]

https://www.oed.com/view/Entry/65505#eid5166397

Answer 2

The principal meaning of the preposition e / ex is just out of, as the corresponding Greek preposition ἐξ / ἐκ.

The great many other different meanings that it has, when joined with words containing specific ideas, follow from a result of the matching. E.g. with the idea of "removing/taking off/empting", the preposition "ex" adds the idea of "completely", like in exhaurio, excavo, epoto (that is, emptying the cup, drinking to the last drop). But I wouldn't say this idea is already in the single preposition "ex".

Before the sense of "former" it was initially used to indicate the origin, "belonging to", without necessarily alluding to a true or definitive exit, like in ex libris, or ex alumnis, or brexit, maybe. The consequent meaning of "former" is not classic, but has become popular in modern times (to the point that "ex" alone today already means "former partner").

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Quotes taken from the comments:

aspice Regulum, qui ex paupere et tenui ad tantas opes per flagitia processit

(Pliny, Epistulae 2.20.13)

Consider Regulus, who, though starting as (i.e., formerly) a poor and humble man, went on to such great wealth through outrageous acts. - @cnread

ex amico fit inimicus, hostis ex socio

(Seneca, Epistulae morales 91.5)

From a friend he became an un-friend, an enemy from an ally. – @cnread