I don't put too much thought into what others look like, so what I might imagine someone to look like is nearly always different than what they do look like, unless their avatar is them or a drawing of them. So if you have an avatar of an old man and keep that around for a while, I'd imagine that it's an old man posting. I won't believe it really is, but I wouldn't really have any other reference to go by unless i've seen their picture. It works for me with photo avatars (even if it's not them), and not so much drawings or whatever.