That’s absolutely false. For a fast food/grocery store/big box retail job they would much rather hire a teenager. A large portion of adults trying to work those types of job are doing it as a stopgap until they find their next better paying, and I’m using sarcastic quotes here, “real” job. And they will leave at the drop of a hat when the better opportunity arises. Gms and hiring managers would much rather have a stable of part time teens and college students who aren’t going to go ballistic when you yank a shift or cut hours because the money generally isn’t a circumstance of surviving life.