Does it creep you out knowing that a man had sex as a minor with another minor? Like, if he lost his virginity at 15 to a 15 yo girl, then he has memories of having sex with a 15yo girl. He probably recalls those memories from time to time. He probably still fantasizes about that 15yo girl, even as a man of 20, 25, 40, 50, etc.
For safety's sake, I would assume such a man has had his mind warped, has a harder time respecting boundaries, and is more likely to be a pedophile. We should reject men who had sex as minors.
It's more problematic if he told it himself. What's the reason other than to triangulate? Does he think it's something to brag about? Another problem is the earlier man starts having sex, the earlier his mental development stops.