Fridge Logic: The events of the respective franchises are not easy to point out, as Jak appears to be around 20 in this game (provided that the game takes place not long after TLF), yet Ratchet (who's suppose to be a year younger) is at least 21 (as it's confirmed to take place between ACIT and A4O, and he's 18 during the events of Deadlocked). And placing Sly in this also brings questions, considering this takes place after Honor Among Thieves, yet in that game Sly retires from thieving by faking amnesia. Not only that, Ratchet and Clank are back in the Solana Galaxy, despite now living in the Polaris Galaxy.
The differences with ageing can be explained: the worlds run on different time axis, explaining why Ratchet aged faster. And as for being in Solana rather than Polaris: it could take place shortly before the comics.
As for Sly's "retirement", this could very well be a warmup heist before the events of Thieves in Time, given Sly was already "feeling the old itch".