It's unrealistic if you're a 5 in looks and overweight. Yeah people may have preferences and that's fine, you like what you like, but that wasn't what you asked. You asked whether your taste was realistic. For example I may want to only date someone who is just like me (same type of personality, same sense of style, same tastes, etc.). There's nothing wrong with that in and of itself, but that doesn't mean that my preference is realistic...because really, what's the chance that I'll get with a person like that? Very slim, lol. So with that said, since your question is only based off of aesthetics, if you're a decent-looking guy with a decent looking body (not necessarily a ten) then it's probably more realistic for you to only want to date petite, athletic-looking girls.
It perfectly acceptable for you to have a preferance of shorter women. I'm 5ft 2 and petite size 4. I've always been contious of my height, was teased a lot for beeing a shorty, it's good to hear that guys find that attractive :)