I was wondering... I have inherited a couple installs that were from back in the 17 or 18 version. I know I cannot do a direct upgrade but if I do a clean install of version 25 and import a backup config from the older versions should I expect any major issues? There has been no settings changed outside of the interface itself so it is just a basic and standard installation with a couple IPSec VPNs configured.
You can always import an old config into a later version. I would do that from the WebGUI after the initial installation.
When the distance between versions is very large, there is a small risk that things might break, but if the config is very simple things will probably just work.