How long do you think pokémon live? Like, will Pikachu outlive Ash or the other way around?
This is an interesting question. I think it probably varies from pokémon species to pokémon species (some dragon types are said to live for thousands of years, but bug pokémon evolve so quickly I would wager they have a few years at most), but as for pikachu specifically …
I think our best guess is to look at the only old pikachu we’ve seen in the anime.
S1E69, “The Pi-Kahuna,” has an old pikachu named Puka. Fortunately for us, we get a flashback to Puka’s youth, back when his trainer first found him:
This was twenty years before the actual episode takes place. Twenty years later, Puka (and his trainer) look like this:
Puka has wrinkles around his eyes, you can’t really see it in this shot but the fur on his ears and tail is a bit ruffled and worn, and he is considerably larger than Ash’s pikachu (though that doesn’t necessarily denote age). Point is, twenty years have passed and not only is Puka still alive, but he has noticeably aged. Not in a drastic way, perhaps—I wouldn’t say he’s that much farther along than his trainer—but he has definitely aged. And while he does have a special connection to the ocean, being a surfing pikachu and all, we have no evidence that affects his lifespan. (And besides, Ash’s pikachu is pretty special as well, what with his enhanced power.)
All we really have is speculation still, but Puka is at least twenty years old and is still going strong, so I would say that Ash and Pikachu likely have many, many more years ahead of them. I would say that pikachu probably have lifespans close to that of the average human (but again, that’s speculation), so the real questions are whether anything other than old age would take either Ash or Pikachu out (they don’t exactly live the safest lives …) and how old Pikachu already is when he and Ash meet. Pikachu very clearly isn’t a baby, after all, even accounting for pichu’s lack of existence in Gen I.
Personally, I like to think that Pikachu was ten years old when they met, just like Ash. Aside from Pikachu being somewhat bratty and immature at times (not used to/confident in battles, not very strong until he gets his power-ups from the lightning bolt in the first episode/charge-up in the Boulder Badge episode, etc), I think it’s just somewhat heartwarming and cute to think they’re the same age. I don’t know, I’m a softy like that. (Plus, like Hiccup and Toothless, I think it’s pretty undeniable that Ash and Pikachu are platonic soul mates, and Hiccup and Toothless are the same age, so …)
So yeah, those are my thoughts! But of course, it’s all speculation, so who knows what the truth actually is. =P
Oh, I forgot about Puka! Those wrinkles make him look older to me than his trainer does, but I guess that doesn’t mean much since we don’t know how old he was when Victor found him (at least that I can remember).
Anyway, thank you for the thoughtful answer!