I am using and older hardware which is not supported on 6.7, but still 6.5 is supported.
How can i get a specific older version with the license key?
All links always guide to latest version
You can't unless you have a purchased entitlement. The free version always defaults to the latest.
https://my.vmware.com/group/vmware/evalcenter?p=free-esxi6
When I am logged in, I have possibilities to download older versions (free ESXi):
the license key is valid for version 6.x - that means no matter if you have 6.0, 6.5 or 5.7 - its the same license