No, I am explaining to you how the system works and how it is used to simulate reality with it's own rules.
It's your interpretation of how the system works, not some objective truth. You call the DnD ruleset a 'reality simulator', which is not how I view it at all. It's a game system, designed to govern + resolve uncertainty in an interactive narrative, and by no means intended as a physically + mathematically accurate modeling of an entire fictional world. If you go at it that way, you should just as well start asking why NPCs don't have full character sheets and are not subject to the same rules regarding actions, spells, etc. - what's the (meta)physical in-world explanation that distinguishes player characters from monsters and NPCs, what makes them essentially different?
IF you would like to actually disprove me then explain how a level 1 fighter and lvl 5 fighter with the same backstory can lead to the level 1 fighter having superior tangible skills. experience and proficiency
You keep comparing character levels, missing my point entirely that it's easily possible to restrict actions from a gameplay point of view, without having to restrict the character's background based on that. Yes, of course that requires somewhat mature players that don't impulsively need to invent "chosen one" backstories with countless great and universe-saving deeds in their pocket (although even that could be managed, provided player, party and DM can agree on how to approach it).
Backstories are *always* subject to DM scrutiny, so I don't even see the risk here that you seem to be seeing. And countless games do this: you start out "weak" in game terms, but your background says otherwise, it's just more fun to progress and 'earn' abilities by what you did in-game, which should however not restrict who your character is as a person entering the adventure, previous life and possible trauma all included without boosting them all the way to Lv 8-12 because of it.
There's simply no reason, neither in the PHB nor in any other objective fashion to decide "we're playing Lv1 characters, so your characters can't be older than xyz years". And yes, bringing adolescence into it logically follows that, because if you're arguing a character that is Lv1 can't have experienced anything useful from a narrative point of view, they have to be very young (or very sheltered) in most cases.
Do you simply not understand that the experiences you have are reflected by your level directly?
I understand your sentiment, but I don't agree that this reflection can ever be as accurate as you obviouly would like it to be, nor that such accuracy should even be attempted. Because again, it's not a simulator (to me). Around a game table, yes, there needs to be consensus about what is believable - fortunately I've been in enough rounds with what obviously would be anathema to you: a party with characters ranging from 16-year-old "just starting out" noobs to grizzled 40-ish mercenary veterans, with quite different ages and experiences, but decidedly not reflected in-game by vastly different character levels - because that would feel much more "wrong" to us (not to mention terribly difficult to balance encounters against). It's perfectly manageable when you're playing with somewhat mature players, and I wholeheartedly recommend it.
