Are older, but Linux compatible computers capable of running the newest kernel/version of various distros?

Guys I truly don't mean to spam the community but these are legit questions. Yesterday I posted about linux compatibility and computers and every single person gave me knowledge to use and you're all awesome.

Now my question is, I will undoubtedly be purchasing an older machine, would an older but good running machine still be able to install the latest kernels or versions of distros or are you limited to older versions only, based on the era of your laptop or is it really about the hardware you have? I know ram, disk space, basic stuff like that matters with distros, but I know that will not be a problem. I guess I'm thinking beyond that like processors. are older processors or anything else hold certain machines from being compatible with the newest and greatest kernels? Thanks!