If you provide the true reason specific to the person why you didn't hire them, and it's an actual job issue they can improve other than "wait until you're 30",

If you provide the true reason specific to the person why you didn't hire them, and it's an actual job issue they can improve other than "wait until you're 30", that's one thing. On the other hand, you said "I now stay away from hiring below 30s." You may have had all kinds of bad experiences after hiring younger folks, but none of those are the fault of the person sitting across the table from you when you interview the next person. You're stereotyping. It's ageism.