I'm 18, he's 30. I'm an unsignificant receptionist at the clinic where he works as doctor. He's cold and distant to me when we're alone, but super friendly when we are with co-workers. Maybe he's shy or whatever, I don't know. Is it normal for me to take interest in a man that acts like this or do I have some daddy-issues I should solve before the ghost of Freud starts hunting me?
And if it is normal, should I show him my feelings and maybe crack his shell open? Or am I just being mental and obsessive about this?
And if it is normal, should I show him my feelings and maybe crack his shell open? Or am I just being mental and obsessive about this?

And he might be acting the way he's acting because you both are at work, and he might notice that you're quite young. One wrong move on his part, could risk him losing his job... well, maybe not that extreme, but... the age difference might be why he's acting so distant. Other coworkers could talk.