Trying to decide what gallery program to use and I'm having trouble finding out if Zen has an option/plugin for albums being 18+ only to view. Any guidance is greatly appreciated!!

You could password protect albums.

There is no built-in age gate or age verification function. If you're savvy with code, GitHub has some age gate scripts you can implement, but I simply use AgeChecker.net and paste the code they give you into the header.php of my gallery's theme. (I run a gallery with 18+ content. I also have my site registered with RTAlabel.org and Age-Label.com just to be safe, and I have tags that warn for content.)