Start with old Desktop with Virtualization extension, something that you can install OS and dont have to remove cause of free space or you need it for something else.
Cause learning Linux or Centos or anything else needs environment, and virtualbox can work but it wont allow you play with KVM, and thats for me the big part of the fun.
Also you need to keep learning that means its is process some day you will leave it 4-5 days dormat cause your stuck in an issue the other day bulb lights up mainly due to reading this site and you get back on it.