I believe the last x86-compatible chips without 64-bit support were launched around 2006 or so (Intel Core; Core 2 had 64-bit support), a couple of years after Opteron initially came out.
It's not really clear how long the Linux kernel itself will continue supporting such CPUs. The architecture certainly isn't something anyone really cares about (e.g. Meltdown wasn't patched for several months after it went public and 64-bit x86 got fixed).
Yup, I bought a brand new 32-bit Intel Atom tablet from Toshiba in 2014, gave it away but the person I gave it to is still using it. It has 32-bit UEFI, which is also loads of fun. I once installed Debian on it, but I couldn't get touchscreen to work, so went back to Windows 8.
It's not really clear how long the Linux kernel itself will continue supporting such CPUs. The architecture certainly isn't something anyone really cares about (e.g. Meltdown wasn't patched for several months after it went public and 64-bit x86 got fixed).