Come on guys. Give em a break. Coming into this as an adult in 2019 I don’t think starting at GS1 is very helpful.
As someone noted I’d start with a sampling of Greatest Hits.
Dark Phoenix - Days of Future Past - God Loves Man Kills as representative of Claremont era.
Then go to Morrison’s New Xmen followed by Whedon’s Astonishing.
These are nice complete stories that nicely build on each other and provide the basis of what Xmen was and how it stands today.
If you are still into it you can just come on board with House of X while filling a few gaps here and there to taste. (My personal favorite is the Paul Smith era of Xmen)