Most plugins will work on versions 1.8.x - 1.18.x. However, there can be some differences in the setup process of different versions (usually legacy vs. modern versions), but we try to maintain the same features across all versions.
Why do you not support version 1.7?
Since the release of 1.8, a lot of new features have been added to the game. In many cases, 1.7 doesn't have an outright alternative. This often leads to spending uneccessary time creating a workaround just for version 1.7. Whats stopping you from upgrading to 1.8 (or later)?
Whats the difference between legacy & modern versions?
Versions 1.12.2 and earlier are considered legacy, while versions 1.13 and later are considered modern.
The method of implementing features for versions 1.13 - latest is usually different from versions 1.7 - 1.12.2. For example, block namings/IDs were mostly changed in version 1.13 when compared to version 1.12.2.