Guy lied about his age

So this guy I just met in class thinks I’m cute and asked me out... I nicely let him down but we still kinda talk as friends. She lied about his age I’m 19 and then turn 20 in feb and he said me too but in the 9th. He def looks older i tried finding his sm and found an old Facebook account and it looks like he graduated hs in 2014 I graduated 2017 this means he’s like 22/23 why couldn’t he tell me this?