I didn't know you had a son. I mean, not like I'm stalking you and keeping tabs on all your personal information, it's just that from the pictures of you I've incidentally observed, I would have guessed you were younger than that.
Ideally, this should be taken as a non-creepy, non-awkward compliment.
But we don't live in an ideal world.
Because if we did, we wouldn't have toys made out of lead.