As long as you don't look like a starving skeleton, it's fine. Some people are naturally thin, but as long as still look a bit "soft" and you can't see bones and muscles moving under your skin, that's fine. There's a big difference between naturally thin and anorexic-looking, which most guys find very unattractive and unhealthy.
You can look great at that size and that slim it would depend on your bone structure. I dated a girl that was 5'2 and 100 lbs and I'm 6'1 185... so ya people date smaller girls haha. Kissing her was funny I could either bend down or pick her up :P