Am I too old to date her?

I'm a 21-year old man, and my place of employment recently hired a 17-year old girl who I'm beginning to fancy. I'm not certain if she was born in '94 or '93, though I'm hoping for the latter. We get along well; we aren't at drastically different mental levels. I still feel a tad odd about pining after a girl who may be 4 years my junior. Should I have my head examined?