Yes but in that example what Craigslist is doing is still legal. It is totally fine to be a person seeking a person including all specific permutations of gender. It's not ok to discriminate based on age for jobs. Facebook has a page for the specific purpose of advertising jobs to people on the basis of their age.
If what you're saying is that they have a purpose built tool to target jobs ads specifically to discreet ages, then it could be problematic --if it's not a dual-use tool.
Not calling out Craigslist --simply illustrating that regular tools meant to be used responsibly can be abused to accomplish nefarious ends.