Thought I was small (actually, super small) growing up due to watching way too much porn way too early (with all the trickery porn directors use to make the male talent look bigger than they are) and also due to being overweight (fat around the pubic area made it seem smaller) and not fully through puberty.
It was only in my 20s, after losing a lot of weight and being more sexually active, that I was told a few times to take it easy because I was "super thick", and my current partner confirmed that I had to be more slow with her because I was "big". I'd say now I realise I may not be anything outside the ordinary length wise, but I am pretty thick - thicker than my own wrists.