No excuse though. Try the “install as oem” of Linux Mint. You get an install with temporary oem account, you can update the system, install additional programs, then click “Prepare for shipping to end user” and on next boot you’re greeted with a setup screen.
Oh, it does: https://wiki.gentoo.org/wiki/Handbook:AMD64/Installation/Disks
Look at that manual, isn’t it nice?