I used Lubuntu for 4-5 years (I don’t recall how long). I switched to MX Linux about a year ago and have been happy with it. I tested a dozen distros (some not lightweight at all, just to compare them to lighter-weight distros). I came down to Peppermint and MX. They both fell in what seemed like the goldilocks zone of lightweight, simple, but not excessively barebones and geeky. I.e., I liked Anti-X & Puppy too. But, they were a little too barebones for me.
Peppermint reminded me a lot of the previous Lubuntu LXDE envirnment. I went with MX Linux because the next version of Peppermint was soon to be released. I didn’t want to install it then upgrade. My plan was to use MX for awhile, then replace it with Peppermint so I could have experience with both. But… I ended up staying with MX because it works fine for me.
You could look at those and see if they accomodate the amount of lightweight and older that you’re seeking. If you really need super-old support, Puppy’s probably the right choice. There may be other distros that are in that category, I forget now. I didn’t need that much minimalism. Just more emphasis on it than Lubuntu was committing to. Peppermint & MX are Xfce desktops. I looked at Xubuntu & Mint Xfce. They didn’t seem to use Xfce for minimalism. Just for people who like X, I think. They both seemed like the new Lubuntu, being lighterweight than the more mainstream distros. But, not really focused on that goal either. Like I said, Peppermint & MX fell more in the goldilocks zone for me. And, Peppermint’s desktop’s look/feel felt more like the previous Lubuntu’s LXDE. It felt like it would be the easiest to get used to.
Both Peppermint & MX have nice forum communities. I spent some time on the Peppermint forum and liked all the people. (I’m feeling guilty writing this as I realize I never did follow through with my plan to switch to it after a few months of MX).
I think the strong point of *ubuntu flavors is the large support community. Ununtu flavors seem to have more of the technical, smart people. (I.e., on Mint’s foum, I’ve seen dead-in-the-water posts go unanswered, whereas you get fast help on the *Ubuntu forums). But, IMO, that cuts both ways. The smart guys are less inclined to “dumb down” the distros to appeal to newbies. Mint’s more inclined to do that. So, it’s a tradeoff that way. Again the two distros I mentioned seemed to fit well in the middle in this regard. A lot of smart, experienced users. And, some pragmatisim toward viewing their distro from the newbie perspective.
I’m not sure why I gravitate toward smaller distros. I’m not running older hardware. I came close to choosing Plasma KDE. It’s look/feel reminded me of OS/2 (which I will never forgive IBM for abandoning – as I make a fist and shake it skyward!). But, I know a lot of people who are cost conscious, cut corners, use hand-me-down hardware. So, I like to support that direction with my own use. I don’t need much eye candy, bells/whistles.