TIL that Slackware is about five months older than me. I was a distro geek in my teens, and Slackware, together with Gentoo, is on of the two distros that I never got working. Is there any concrete advantages to using it today?
As a new slackware user, I see the following advantages
1. no systemd
2. really minimal bare system: running htop shows less than 10 processes running (including those of root)
3. simple package management with no dependencies: a "package" is just a tgz file that you decompress into your filesystem
4. very up to date binary packages (e.g., there are just few days between the release of a new gcc version and its availability as a slackware package).
I have spent most on my life on debian and ubuntu, and I cannot imagine going back to them. Other distributions that I like are voidlinux (but unfortunately it has automatic package dependences, that limit my freedom too much) and dragonflybsd, which has also very modern packages.