I monitor closely my Internet connection (since I serve stuff on it, and also because why not) and I saw my IP changing and wandering throughout the Ile-de-France. I would say that the changes are every 6 months or so (since one of my domain is with Gandi I had to write a checker and change the assignment through their API)
If you only use IPv4, then these days (with not only the Asiatic countries never having got IPv4, but Europe having ran out if IPv4 addresses), technically you don't have a "real" Internet connection any more.
My bad, I should have said that "some" Asian countries never had enough IPv4 addresses to start with. AFAIK this explains why India is one of the world leaders in IPv6 deployment ?
(I've also heard that IPv6-only networks are not uncommon in some Asiatic countries ?)
IPv6 has been slowly rolled out for more than a decade now, though AFAIK the standard has only been finalized in 2017.
Since 2017, first choice should have been IPv6.
"Internet" stands for "International network". If you're using IPv4 only, when someone else uses IPv6 only, then obviously you won't be able to connect to each other. Therefore you aren't on the same network. And only one of them can be "really" called "Internet".
(Also, IPv4 was an experimental ARPANET protocol which wasn't supposed to be used "in production" worldwide, but here we are...)
