Why would he lie about his age?

So last week i had a night out and I met this really sweet guy. I added his number and snapchat before we went home (separate i was on my period) I didn’t expect to hear from him, ive been single ages and I don’t hear from most guys i swap numbers with but he has been messaging me everyday since.

My friend stayed over Saturday as shes having marital issues and needed a break, she looked this guy up on Facebook (i hardly bother with fb atm) and he is 10 years younger than he told me he was... I’m not one to be bothered with age gaps as long as they are legal, it bothers me he lied though and I don’t know what to think about it? Like why would he say he is older?

He’s mature for his age and everyone says I’m young for mine... I don’t get it?