I'm not sure the post count that makes it so you can pm, I got 10 post count and still couldn't. (I think a few of those posts were removed? Maybe because they weren't quality posts lmao).
In my opinion allow anyone to pm but limit the pm's per hour a bit more, or maybe mod the site to allow 1pm per personal message they have received if they are not up to the correct post count yet.
IDK just a suggestion, it's really just a minor nuisance haha