Linux. Take an easy distribution like Ubuntu or Mint.
Discussion
So reconfigure an old windows into Linux? Would that be good for starters.. or get a new laptop.. not the latest one, but something a year old?
You can install almost every Linux as dual-boot together with Windows. Ubuntu-based distros offer an option at setup to choose this. So you can keep your existing Windows installation. Then you get a boot menu where you can decide whether you want to boot into Linux or Windows at the start of your machine.
Every hardware is suitable for Linux. One year old is nothing, still considered new.