Remove files that start with but don't contain

Yes you can use more than one pattern with find:

$ find -name 'master-*' \! -name 'master-2018*' -print0 -prune |
     xargs -0 echo rm -fr

(remove the echo if you're satisfied with the dry run)

You should add a -maxdepth 1 predicate just after find if you only want ro remove files from the current directory, ie master-1991 but no subdir/master-1991.

In bash:

shopt -s extglob
echo rm master-!(2018*)

Remove the echo if it looks correct.

The above uses bash's extended globbing facility to match files that start with master- but who do not have 2018 immediately following, then followed by anything (*).