No PDA
With guys in their early twenties, you expect them to not be totally comfortable being lovey-dovey yet. They’re still trying to prove they’re a “man.” But, later, if a man you’re dating refuses to hold your hand in public, you know it’s not really a good thing. He might have trouble being affectionate and caring in general or he cares too much about what other people think. Essentially, all things that would make a relationship with him difficult.