I feel like they shouldn't be lyin'. I've never actually known anyone who did that or anyone that it happened to though. I did know guys in their 20s that would weirdly brag about really young girls having crushes on them / feelings for them that they were not going to reciprocate or encourage. As if they were super amazing humans for not taking advantage of a 14-year-old child. The bar must be so low that it's in the core of the earth if that's what makes them feel like they've gone above and beyond.
Why even lie about age? Did they really think that the person they're dating won't discover the truth? I mean, why lie about something that is inevitable to be discovered? Acceptance is the key while honesty is a requirement for a relationship to work well. How can you be with someone who can't even be honest with trivial stuffs like his age?