Correction: Why - in your opinion - *are there* some people who refuse to show their age on any social media *network*?
Here in the US, identity theft is a huge problem that's a nightmare to fix. If someone has your name, your age and other personal details about you (your city, for instance) , they can open credit accounts in your name, steal your tax return, and basically ruin your financial history. Without a good credit history, you can't buy a house or take out a student loan.