"
Things Mr. Welch Is Not Allowed to Do in an RPG" is probably the earliest
offender example of such lists and definitely predates both of those.
(TVTropes link warning: reader discretion is advised.)
I believe Mr. Welch is indeed the originator of the 'Things X Is Not Allowed To Do' lists, at least on the internet.
I wouldn't be surprised if similar jokes existed in meatspace prior, but if so none of them made the transition to the intertubular webs that I know of.
Even that is a bit far – "physically" it only makes no sense if we take for granted that aging, and life, work the same way as they do IRL, cell division gradually failing over time for reasons caused by accumulated damage rather than something drainable. Maybe in one setting, aging does work like that, but life-draining causes premature aging anyway for thematic reasons, as you say.
In another setting, maybe cells don't exist. Every soul has a predetermined maximum lifespan which can only be known when it runs out. Life-drain magic winds your clock forward to turn someone else's back, stealing sand from Death's hourglass to prolong or shorten life regardless of the state of the body that a soul is in – that makes for interesting story things, a person who's doomed to die when they're young and healthy, another who's decrepit or injured but can't actually die for years to come. Perhaps you get body-horror that way, or perhaps you just get zombies and ghosts. Would ghosts seek out zombies, to have a body again even if it's not "theirs"? What happens when one succeeds at that?
In another setting, perhaps life is a conserved quantity, from plants to animals to rot and back to plants, aging is caused by the accumulated losses through various waste products and/or blood loss from injury. There, life-drain is vampirism, and perhaps some people will be unwilling to kill others yet sufficiently afraid of death to take extreme measures such as collecting and drinking as much as possible of whatever blood they spill in their own injuries – hey, now you've got a creepy-to-the-reader religion, perhaps.
Or it's little intangible imps latching onto and cursing people who get their attention, and life-drain isn't actually taking something from someone else, it's convincing the imps on you to go curse someone else for a while. Now there's an agent involved, and people can start trying to work out how it thinks (no two imps have quite the same interest), and there can be philosophies and/or self-help scams focused on trying to avoid imp-interesting activities (varyingly effective but usually not much; someone so afraid of death that they never do anything interesting is thereby made interesting by their obsession and uniquely extreme dullness), and the imp-transfer magic requires a lot of consideration of your own mortality to know what your imps are looking for, and of your target to be sure your imps would like them, and now you've got a personal relationship with the person whose life you're stealing as well as with the being you're trying to get rid of.
Magic can be defined, and fundamental to the world at a low level, and yet not readily science-able. It works on a scale or through a medium that cannot be directly observed, or it closely involves the decisions of myriad spirits and thus turns into a variant of psychology. Maybe it can be known but is not; people have found ways to see the soul but every soul is so individual that nobody's yet figured out how to tell how much time someone has left. The fantasy doesn't go away, and neither does the story, and yet you're not getting into a Sanderson-like hard-fantasy thing with rules the reader can be expected to use to anticipate events before the story gets there.
I'll be honest; I have no idea what you are trying to get at here as a response to my post.
Physics is 'the knowledge of nature', aka 'how reality works'. If you live in a reality where magic exists, then magic is part of reality and thus understanding how magic works is, at a basic level, physics.
Other disciplines might be involved, like the psychology example you gave, but those are
on top of the physics of the magic.
Magic being explained in-setting also doesn't make 'the fantasy go away', it just gives the reader a framework for the story, which can be good or bad for immersion depending on execution.
Ultimately however,
most of the times you see 'magic' in fiction, it's not
actually magic. 'Magic' is a code-word that means 'I don't understand how it works' or 'I'm not going to tell you how it works'. If it is understood and\or explained, then it's technically not
really magic anymore. Because magic is, at it's core,
a mystery.
Ancient humans pointed at all the things they saw happening and did not understand and called those things magic, because it sounded less embarrassing than admitting they hadn't the faintest fucking clue what was going on. And that is why modern humans point to things like computers and call
them magic in a semi-joking manner, because to many people, they
are magic: A thing that happens\works and they do not understand why or how.
Generally speaking, in fiction, 'magic' is instead used as a codeword for 'the ability to alter reality', often by thinking really hard at it and requiring some kind of metaphysical 'mana' energy. This is,
strictly speaking, not magic; it is imaginary physics. But magic gets the point across easily and is a much neater term than 'reality warping', so popular culture agrees to use magic for that sort of thing, because why not.
