Max Level for Sidekicks (dict)
From Twilight Heroes Wiki
Max Level for Sidekicks
n. Sidekicks don't have levels, they progress along with you as you level. This is the maximum level for you (meaning your level) at which the sidekick (meaning them) will improve over the previous level (still your level). Above this level (your level) the sidekick won't get any better at what they do.
Source
Clicking on the asterisk next to Max Level on the Sidekick page of the hideout.