Why would people lie about being younger than they are? That doesn't make any sense. He looks like a teen.
And you're basing this off of what exactly? Sure it's creepy and forgeted up, but you're just assuming he's over 18.
in the context of your classic internet argument you wouldn't want to lie about being younger than you really are, sure
but when you're a child enthusiast, the purpose of coming off as younger than you really are is to make yourself seem closer with the minor in question. people of a similar age draw eachother in, obviously, so if someone says they're 15 and they're into all these neat little things like furries and anime and videogames then surely other 15 y/o's who are furries and weebs and gamers will also be drawn to them.
tl;dr
“hey im 37 years old”
“ew forget off creep”
vs
“hey im 15”
“dude, nice”
there was a picture posted that was supposedly him. is that the only one he's posted? or one of few? did anyone reverse search it to make sure it wasn't some random kid that was picked off of facebook or something?