Well, I started lying about my age when I was young. People refused to believe how old I was so I started saying I was older than I actually am. Then I didnt get accused of lying so much.
People sometimes judge you because of your age. Which I have seen even on gupshup. That is probably why many women lie and say they are younger than they actually are. I've also known men online to lie about their age. They refuse to go past the 29 number. They'd only tell me their real age when they thought I would speak to them regardless of their age. (Experienced this in my chat days, no longer, but I think it probably hasnt changed much since then.)
Actors/Talent/models are sometimes encouraged to lie about their age, to get jobs.