This is an unedited paste of an email I sent to kappa a while ago.
Subject: on the fact that you can beat a pokemon game in less than a full day of play time
I have been contemplating various reasons why this would not be possible to do with real live pokemon in Arceus. Here are thoughts.
1. Basic videogame streamlining (where your character doesn't have to eat, sleep, doesn't care about getting rained on, always wears the same clothes, etc.) is not in effect, obviously. Same for your 'mon. This takes up plenty of time, and money (and acquiring money takes time).
2. Difficulty levels are not ordered in a neat linear path or skewed in your favor or neatly mathematical with health bars and levels. People just starting out probably have a lot of legit trouble finding challenges appropriate for their 'mon to learn from without getting just beat to hell and back. You probably need a decently well-trained 'mon (as opposed to one that just hatched) just to leave inhabited areas without being pecked to death by the local Extremely Common Bird Pokémon. Also, on average, people lose half their battles. You do not unleash a full team of six on random people who only have two, you do not beat up the last 'mon of someone in a wilderness situation, the rules are not lopsided so you can swap for type advantage as much as you want and everybody else leaves their 'mon out until you defeat them barring special circumstances, and your opponents do not act at near-random from a badly curated moveset.
3. 'Mon grow slower in real life. Maybe they can get out of shape and/or out of practice - not de-evolving, but maybe forgetting moves that aren't practiced, and definitely dropping in the real-life equivalent of stats - if they don't get plenty of exercise and practice, much of which needn't (indeed, shouldn't) be in actual battles. They also have more features to cultivate than just attack/defense/sp. atk./sp. def./speed - it matters how smart they are, how good they are at informal scuffling between moves, the fact that the moves aren't turn based in reality means that there's more flexibility about timing and how they're executed, probably 'mon miss more often in real life and there's also more of a thing of grazing shots and less of a thing of critical hits. It seems likely not all battles are fought to fainting. And your 'mon don't give a shit how many badges you have when they are deciding whether to obey you; they have to be convinced to do what you say separately, both in terms of battle moves and in terms of approximately behaving elsewise, with relatively recognizeable animal training methods and some higher reasoning faculties if the mon is smart.
4. In the games people give you a fuck of a lot of stuff and there is also a lot of stuff on the ground. This does not happen in real life. Also, people do not actually bet half their life savings on every battle they undertake - or usually at all, outside of formal tournaments with tiers and other mechanisms to make it fair. By and large you have to get your money for your Pokéballs and your medicine and such via producing actual economic value or an allowance from your parents or something. (I'm now imagining most towns having bulletin boards or some kind of electronic equivalent with odd jobs for trainers with specific Pokémon or classes thereof to take.) Also, things are more expensive relative to how much income you get - in the games you can pretty much afford to catch at least one of every species you see, in real life that should be untenable on grounds of pure economics for most people, collecting should be *expensive* for the Pokéballs alone even if you don't count the effort put into finding all these 'mon.
5. Everything is bigger - towns, stretches of wilderness, roads, oceans - and there aren't impassable forms of terrain keeping you on your railroad. You can probably actually make some progress at not being a complete incompetent in the environs of your hometown, but this will limit your selection of what you can catch pretty sharply and you won't be able to collect badges that way, so mostly you have to hike or ride 'mon over long distances if you want to be more than a hobbyist-with-a-rodent-and-a-bird. Also, I think that in spite of Ace's incredulity that her game will not let her sit on and ride arbitrary quadrupeds and birds, very very small 'mon that can learn (e.g.) Fly in the games cannot necessarily pick you up and carry you (or maybe they can - mon are deceptively strong - but it won't be comfy to be picked up and hauled by a one foot tall Fletchling).
6. While Pokémon centers exist (and I think they should have a hostel function the way they do in anime), the fact that everything is bigger means it's harder to get to one quickly, and the fact that wild 'mon can actually fucking kill you if you are caught without your own 'mon to defend you means that you need to be very well stocked on your 'mon meds, which contributes to your economic problems. Sleeping it off also works, but not as fast as it does when you find usable napping places in games, and you may be attacked by 'mon in the night if you're bivouacking. (Also, you can encounter wild 'mon while flying from place to place that want to make trouble; same if you are digging somewhere, which is also slower and less convenient than it is in games.)
7. All that said, the game is also harder in a couple ways. I think you should be able to catch a fainted 'mon in Arceus which you cannot do in games; most trainers do not have to address organized crime just to enter cities they wish to visit; it should be possible, if difficult, to talk a 'mon into belonging to you without formally catching it; there are various organizations like the Ace Trainers to which Ace belongs which pool poolable resources. And your 'mon will not love you less if you lose battles (in the games, your friendship level drops if they faint, at all ever, which I do not think would be reasonable for non game protagonist trainers and which kind of undermines the "mon do not mind being in frequent gladiatorial combat" thing).
All that said, it still doesn't take that long to "beat the game" in real life - most people have a 'mon (just so they can leave the house without being in danger from the equivalent of pigeons; city 'mon are probably pretty tame but why risk it?) by the age of ten, and probably most League champs are under age eighteen with a decent fraction being under sixteen. Ace had a bit of a leg up because Zag came to her partially trained and because she can maintain a hold on a full six 'mon all at once while others might be trying to balance and work with necessarily smaller teams at a time. Her mon being the equivalent of level-fifty-plus while she is fifteen shows dedication (in her case, she's mostly working on a side project, but one that requires a lot of travel and therefore keeps her mon in good shape) but not superhuman prowess.
(the fact that you need a 'mon just to go anywhere probably means that most people aren't "trainers" even if they have one or two Pokémon, in much the same way most people do not refer to themselves as "cooks" even if they know like four recipes. "Trainers" are people who have three or more personal (as opposed to farmed or something) 'mon, or at least occasionally battle for fun, does that sound right to you?) (Some 'mon, as species or individuals, are possible to keep roughly like domestic herd animals for milk or wool or beasts of burden for riding around on or whatever. Miltank for milk, Chansey for eggs; situations like in Y where you ride a particular docile Rhyhorn or Mamoswine should not be outrageous.)