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!
Nearly all hardware support is kept in the kernel until and unless it bitrots to the point of unusability. I've had no issues with a 5.10-series kernel on my 2008 laptop, and I don't expect any issues when I finally get around to upgrading it to 6.x (well, except the usual tedium of compiling a kernel on a machine that weak).
But running an older kernel, wouldn't you get an older "experience", perhaps less features, etc.?
The difference isn't all that noticeable, to be honest, or at least I've never found it so. If you're using older hardware, you're going to get an older "experience" anyway. The most user-visible kernel improvements tend to be improvements in hardware support, which is irrelevant if your hardware is already fully supported. However, I don't do anything fancy with my machines—no full-disc encryption or the like. I usually don't even need an initram to boot the system. So maybe you would notice something if your machines were more complicated.
(Note that the laptop I mentioned above started out with, um, a 3.x kernel? It gets a new one every year or so. The only kernel changes affecting it that were significant enough to draw my attention since 2008 were a fix in the support for the Broadcom wireless card it carries, and some changes to how hibernation works, which didn't matter in the end because I basically never did try all that hard to get hibernation working on that machine.)
See I fear this, being stuck to only kernels up to a certain version. Because don't the older ones lose support and stuff like that? how the heck do you maintain your system if the distro isn't pushing anymore updates and such?
You're unlikely to have issues unless an entire architecture loses support from your distro, and if you're running x86_64, that isn't going to happen for a long, long time. I've never been in a position where I couldn't compile a new workable kernel for an existing system out of Gentoo's repositories. The only time I've ever needed to put an upgrade aside for a few months involved a machine's video card losing driver support from nvidia—I needed a few spare hours to make sure there were no issues while over to nouveau before I could install a new kernel.
Note that you can run an up-to-date userland on an older kernel, too, provided you make sensible software choices. Changes to the kernel are not supposed to break userspace—that's meant to keep older software running on newer kernels, but it also works the other way around quite a bit of the time.