Probably Konoha Twelve are late teens/early twenties. So old enough to have some level of independence, but young enough that they aren’t expected to be taking over for their parents already.
As for whether or not Naruto will outlive them… I’m still on the fence about what exactly he is. Like, if he’s entirely a coded copy of the child Naruto that learned and developed (in which case is he still Naruto or just a copy) or if he is mentally connected to the robot body and his real body is somewhere, or if he’s actually a really advanced cyborg and his brain and some other organs are inside of the robot body but not so much so that there aren’t uncertainties of his humanity? I don’t know.